Alkoxy(tetraaryl)silicates bearing 9,10-disilatriptycene skeleton

Article abstract of DOI:10.1002/hc.21481

As anionic five-coordinate silicon species (five-coordinate silicates) exhibit high reactivity and unique fluxional behavior, their structure and property have received substantial attention. We report herein synthesis, structure, and fluxional behavior o

Full text of DOI:10.1002/hc.21481

Received: 1 October 2018
DOI: 10.1002/hc.21481
Revised: 22 November 2018
Accepted: 22 November 2018
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S P E C I A L I S S U E A R T I C L E
Alkoxy(tetraaryl)silicates bearing 9,10-disilatriptycene skeleton
Shintaro Ishida
Minori Takiguchi
Takeaki Iwamoto
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Department of Chemistry, Graduate School
of Science, Tohoku University, Sendai,
Japan
Abstract
As anionic five-coordinate silicon species (five-coordinate silicates) exhibit high re-
activity and unique fluxional behavior, their structure and property have received
substantial attention. We report herein synthesis, structure, and fluxional behavior of
alkoxy(tetraaryl)silicates having the 9,10-disilatriptycene skeleton (6− and 7−). The
molecular structure of the cryptate salt [Li(crypt-222)]+7− shows that the five-
coordinate silicon adopts a distorted trigonal bipyramidal structure with oxygen atom
occupying an equatorial position. In the 1H and 13C{1H} NMR spectra of
[Li(crypt-222)]+7−, a set of signals due to o-phenylene blades in 7− was observed at
room temperature, which indicates fluxional behavior of 7− on the NMR timescale.
Computational study suggests that the observed process proceeds via a 120° rotation
of bidentate ligand around the Si-Si axis that consists of two sequential Berry
pseudorotations.
Correspondence
Shintaro Ishida and Takeaki Iwamoto,
Department of Chemistry, Graduate School
of Science, Tohoku University, Sendai,
Japan.
Emails: ishida@tohoku.ac.jp; takeaki.
iwamoto.b8@tohoku.ac.jp
ligands (Figure 1)[9] indicate that stereomutations of anionic
five-coordinate silicates are greatly influenced by the bidentate
1
INTRODUCTION
|
Four-coordinate silicon can accept a nucleophile to form five-
coordinate silicon species (five-coordinate silicates).[1] Because
silicates are regarded as key intermediates for numerous reac-
tions such as Tamao oxidation,[2] Hiyama coupling,[3] silyl mi-
grations,[4] and dehydrogenative silylation,[5] their structure and
property have attracted considerable attention even in recent
years. In general, five-coordinate silicates prefer trigonal bipy-
ramidal geometries and exhibit a facile fluxional behavior due
to the intramolecular stereomutation with a small activation bar-
rier. This process is interpreted as a Berry pseudorotation (BPR)
that proceeds via a square pyramidal structure during molecular
motion as shown in Scheme 1.[1,6] Although turnstile rotation
(TR) between three ligands (trio) and two ligands (duo) was pro-
posed as another possible mechanism to explain the fluxional
behavior,[7] Couzijn and Lammertsma[8] have revealed that TR
is equivalent to BPR by a topological analysis.
ligands. In group-15 element chemistry, five-coordinate anti-
mony compounds I and J having rigid tridentate ligand exhibit
fluxional behavior due to the TR induced by the geometrical
constraint.[10,11] Therefore, anionic five-coordinate silicates
bearing tridentate ligands should give further information on
their fluxionality and the mechanisms of stereomutation.
Previously, we reported
a
facile synthesis of
9-phenyl-9,10-disilatriptycene (1) by the reaction of bis(2-
bromophenyl)silane (2) with magnesium under a microwave
heating condition (Scheme 2).[12] As Grignard reagent 3
formed as an intermediate in this reaction, a functional group
can be introduced on the 2-position of the external phenyl
ring. Thus, we planned to synthesize alkoxy(tetraaryl)sili-
cates having 9,10-disilatriptycene skeleton (Figure 2) that
1
1
M
2
3
M
4
1
2
Several studies on the dynamic behavior of well-designed
anionic five-coordinate silicates A-H having two bidentate
3
M
4
3
3
4
2
1
5
5
M
5
5
≡
4
Dedicated to 82nd birthday of Professor Naomichi Furukawa.
Contract grant sponsor: JSPS KAKENHI
Contract grant number: JP25708004
2
Square Pyramid
SCHEME 1 Berry pseudorotation of five-coordinate species
Contract grant number: JP25620020
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Heteroatom Chemistry. 2018;e21481.
https://doi.org/10.1002/hc.21481
wileyonlinelibrary.com/journal/hc
© 2018 Wiley Periodicals, Inc.
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ISHIDA et Al.
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N
N
N
N
X
Me
Me
R
Si
Si
Si
Si
A:
B:
=
=
D
E
C
X
X
F
Me
CF3
O
F
3C CF3
S
O
O
Si
O
O
O
O
Ar1
R
R
Si
Sb
Ar2
R
Si
FIGURE 1 Structurally constrained
anionic five-coordinate silicates A-H
and neutral five-coordinate stiboranes
I and J having a tridentate ligand
(Ar1 = 3,5-Me2C6H3)
O
2
F
3C CF3
G
I:
J:
=
4-
O
Ar
H4
ClC6
H4
CF3C6
S
2
H
=
4-
Ar
F
Br
SiH2
Br
MgBr
hydride reduction of 4 with LiAlH4 afforded 5 in 83% yield.
Structures of 4 and 5 were determined by a combination of
NMR spectroscopy, MS spectrometry, single crystal X-ray
diffraction (XRD) study, and elemental analysis.
(i)
(ii)
2
H
H
Si
Si
Si
Si
2
3
1
SCHEME 2 Synthesis of 1 via 3. (i) Mg, THF, reflux or
Treatment of 5 with an equimolar amount of tert-
butyllithiuminTHFat−78°Caffordeddesiredfive-coordinate
silicate salt [Li(thf)]+6− in 80% yield (Scheme 4). A similar
reaction of 5 with two equivalent of tert-butyllithium gave
tert-butylated silicate [Li(thf)]+7− in 82%. In this reaction,
the second tert-butyllithium reacted as a nucleophile toward
the Si–H moiety of 6−. Hydrolysis of [Li(thf)]+7− gave ben-
zylalcohol derivative 8 in 62% yield. Exchange of the ligand
on the lithium cation from THF to [2.2.2]cryptand (abbre-
viated as crypt-222) increased the stability and crystallinity
of the silicate, and [Li(crypt-222)]+ 7− salt was successfully
isolated and spectroscopically and structurally characterized.
microwave heating (150°C); (ii) aqueous work-up
O
Si
O
Si
H
Si
Si tBu
7−
6−
FIGURE 2 Alkoxy(tetraaryl)silicates 6− and 7−
would give information on the dynamics behavior derived
by the combination of the rigid tridentate and bidentate li-
gands on the five-coordinate silicon. We report herein (a)
synthesis of new alkoxy(tetraaryl)silicates 6− and 7− having
9,10-disilatriptycene skeleton, (b) molecular structure of
[Li(crypt-222)]+7− (crypt-222 = [2.2.2]cryptand), and (c)
dynamic behavior of 7− in solution. In addition, fundamen-
tal properties of the newly synthesized 9,10-disilatriptycene
derivatives are also presented.
2.2
Molecular structures of neutral
|
9,10-disilatriptycenes
Solid state structures of neutral 9,10-disilatriptycene de-
rivatives (4, 5, 8) are shown in Figures 3-5. In compounds
4, 5 and 8, the closest distances between oxygen and sili-
con atoms (intramolecular O1 and Si1 distances) are 4.38,
4.26, and 4.26 Å, respectively. These distances are much
longer than the sum of the van der Waals radii (ΣrvdW
)
of silicon and oxygen atoms (3.62 Å).[14] Thus, no sig-
nificant bonding interaction exists between these atoms.
Hydrogen bonding of hydroxy groups was not found in the
crystal of 5; the shortest intermolecular distance between
oxygen atoms was 7.54 Å, while dimeric structure by hy-
drogen bonding was observed in the packing diagram of
8 (intermolecular O···O distance of 2.63 Å, Figure S2).
The averaged bond lengths of Si1–C(o-phenylene) and
2
RESULTS AND DISCUSSION
Synthesis
|
2.1
|
As shown in Scheme 3, 2-formylphenyl derivative 4 was pre-
pared by the reaction of in situ generated 3 from 2[13] with
DMF in 18% isolated yield (based on 2). The subsequent

ISHIDA et Al.
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OH
Si
CHO
Si
(i)
(ii)
2
H
H
Si
Si
4
5
(83%)
(18%)
SCHEME 3 Synthesis of 4 and 5. (i) THF reflux with Mg,
followed by excess DMF at 0°C for 1 h; (ii) ether with LiAlH4 (0.5 eq.)
at 0°C for 40 min
+ 6−
(i)
[Li(thf)]
(80%)
(iii)
+ 7−
5
[Li(crypt-222)]
(82%)
FIGURE 4 Molecular structure of 5. Hydrogen atoms are
+ 7−
(ii)
omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level. Selected bond lengths (Å) and angles (°); Si1–C1 1.877(4),
Si1–C8 1.890(4), Si1–C14 1.898(4), Si1–C20 1.899(4), C1–Si1–C8
112.45(17), C1–Si1–C14 117.08(18), C8–Si1–C14 102.45(17),
C1–Si1–C20 116.79(18), C8–Si1–C20 104.96(17), C14–Si1–C20
101.31(17)
[Li(thf)]
(82%)
OH
Si
(iv)
Si tBu
8
(62%)
SCHEME 4 Synthesis of silicates 6− and 7− and benzyl alcohol
8. (i) tert-Butyllithium (1.0 eq.) in THF, −78°C for 1 h; (ii) tert-
butyllithium (2.3 eq.) in THF, −78°C for 1 h; (iii) crypt-222 (1.0 eq.)
in toluene at room temperature for 1 day. (iv) Aqueous work-up
FIGURE 5 Molecular structure of 8. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level. A disorder was found in the OH moiety with the occupancy
factors of 0.51 and 0.49, and a hydroxy group is shown. Selected bond
lengths (Å) and angles (°); Si1–C1 1.8828(17), Si1–C8 1.8797(17),
Si1–C14 1.8885(16), Si1–C20 1.8806(17), C1–Si1–C8 115.63(8), C1–
Si1–C14 121.32(7), C1–Si1–C20 107.96(7), C8–Si1–C14 100.66(7),
C8–Si1–C20 105.08(7), C14–Si1–C20 104.64(7)
FIGURE 3 Molecular structure of 4. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level. Selected bond lengths (Å) and angles (°); Si1–C1 1.881(2),
Si1–C8 1.890(2), Si1–C14 1.894(2), Si1–C20 1.895(2), C1–Si1–C8
115.40(9), C1–Si1–C14 110.92(9), C8–Si1–C14 103.71(9), C1–Si1–
C20 118.52(9), C8–Si1–C20 103.02(9), C14–Si1–C20 103.62(9)
2.3 | Molecular structure of silicate
Molecular structure of [Li(crypt-222)]+7− obtained by XRD
analysis revealed that the salt is a solvent separated ion pair;
the cationic part [Li(crypt-222)]+ is well-separated from the
counter anion (Figure S1). In anion part, oxygen atom (O1)
coordinates to silicon (Si1) to form a five-coordinate silicate
as shown in Figure 6; the Si1−O1 length of 1.7428(14) Å is
Si1–C(2-substituted phenyl) [1.891(3) and 1.880(3) Å]
are slightly elongated from the standard Si–C bond length
of 1.86 Å.

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ISHIDA et Al.
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having one axial ligand of C8 and four basal ligands (O1, C1,
C14, C20). Shorter bond length of Si1–C8 compared to the
other Si1–C bonds and a relatively long Si1–O1 bond support
that the SP character of 7− despite the large %TBP values. The
observed deformation to the SP structure may arise from the
packing forces in the single crystal because several intermolec-
ular contacts between the bidentate ligand of 7− and neighbor-
ing molecules were observed. To the best of our knowledge,
[Li(crypt-222)]+7− is the first isolable alkoxy(tetraaryl)silicate.
(a)
2.4
UV-vis absorption and
|
fluorescence spectra
Since UV-vis absorption and emission of several arylsilanes are
dependent on the number of the coordination of nucleophiles to
form anionic silicates,[18] we investigated absorption and emis-
sion of compounds 4-8. Absorption and fluorescence maxima of
9,10-disilatriptycenes 4, 5, 8, and [Li(crypt-222)]+7− are sum-
marized in Table 1, and their spectra are shown in Figures S3-
S6 in the Supporting Information. UV-vis absorption spectra of
neutral compounds 4, 5, and 8 exhibited intense bands around
215 nm and weak bands (1Lb band) around 275 nm. The posi-
tion of 1Lb band of anionic silicate [Li(crypt-222)]+7− (276 nm)
is not significantly shifted compared to those of the neutral spe-
cies. In compound 4, an additional very weak absorption band
due to n→π* transition appeared around 343 nm. In the fluores-
cence spectra, a broad emission band of [Li(crypt-222)]+7− ap-
peared around 350 nm, and the position of the band was similar
to those of 5 and 8. Consequently, coordination of alkoxide to
the silicon atom of 9,10-disilatriptycene skeleton to form ani-
onic silicate does not remarkably affect the absorption and fluo-
rescence spectra. Compound 4 was nonfluorescent as well as
common aryl carbonyl compounds.[19]
(b)
FIGURE 6 A, Molecular structure of [Li(crypt-222)]+7−.
Counter cation [Li(crypt-222)]+ and hydrogen atoms are omitted for
clarity. Thermal ellipsoids are drawn at the 50% probability level. B,
Bond lengths (Å) and angles (°) around five-coordinate silicon (Si1)
longer than standard tetracoordinate Si–O bonds (1.64 Å) and
much shorter than the ΣrvdW of Si and O atoms (3.62 Å).[14]
A
large bond angle of C1–Si1–C20 [161.45(9)°] indicates that
C1 and C20 atoms occupied the apical positions. To evaluate
five-coordinate geometry of 7−, the indicators of the trigonal
bipyramid geometry (%TBPa and %TBPe)[15,16] were used.
The %TBPa values for C1 and C20 are 87.0 for C1 and 97.9
for C20, and %TBPe of 99.6 indicate that five-coordinate sili-
con of 7− adopts a distorted trigonal bipyramidal geometry.
As the bidentate ligand is positioned on space between two
o-phenylene blades (C8 and C14) of 9,10-disilatriptycene
skeleton to avoid steric congestion, the electronegative O1
atom of the bidentate ligand occupied an equatorial position
against the Muetterties rule.[1,17] The Si–C bond lengths of
five-coordinate silicon are elongated compared to those of tet-
racoordinate compounds (4, 5, and 8); the apical Si–C bonds
(Si1–C20 and Si1–C1) of 2.014(2) and 1.982(2) Å are longer
than those of the equatorial Si–C bonds [Si1–C8 and Si1–C14
1.910(2) and 1.977(2) Å] in 7−. As shown in Figure 6B, a re-
markable large bond angle of O1–Si1–C14 [150.36(8)°] from
that of O1–Si1–C8 [108.32(8)°] indicates that TBP structure
of 7− deforms somewhat to a square pyramidal (SP) structure
2.5
Molecular structures in solution
|
29Si NMR chemical shifts of 9,10-disilatriptycenes (4-
8) are summarized in Table 2. The 29Si NMR signals of
TABLE 1 Photophysical parameters of 4, 5, [Li(crypt-222)]+7−,
and 8
Compound
4a
λmax/nm (ε/mol−1 dm3 cm−1
)
λemc/nm
213 (1.0 × 105), 281
Not
detected
(3.0 × 103), 343 (7.0 × 10)
5a
215 (8.1 × 104), 274
356
353
349
(1.9 × 103)
8a
215 (8.0 × 104), 274
(1.7 × 103)
[Li(crypt-222)]+7−b
276 (2.8 × 103)
aIn hexane.
bIn THF.
cExcited at 250 nm.

ISHIDA et Al.
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TABLE 2 29Si NMR signals of 9,10-disilatriptycenes
on the temperature dependence of the fluxional behavior of
[Li(crypt-222)]+7− in THF-d8. In the H NMR spectra of
1
R
[Li(crypt-222)]+7− at various temperatures, signals of blades
split into two sets of signals with 2:1 integral ratio in lower tem-
peratures (Figure 8). The rate constants of the dynamic process
at each temperature can be determined by line-shape analysis
using well-separated signals of 8.37 and 7.06 ppm at 193 K, and
the kinetic parameters for the dynamic behavior derived from an
Eyring plot (Table S5) were as follows: ΔH‡ = 40.5 0.9 kJ/
mol and ΔS‡ = −8.8 4.1 J mol−1 K−1. The small ΔS‡ value is
consistent with an intramolecular process.
O
Si
R'
Si
Si
R'
Si
6−
7−
:
4
:
5
:
8
R =
R =
R =
R' = H
:
:
CHO,
R' = H
R' = tBu
H
H
R' = H
C
2OH,
2OH,
R' = tBu
C
Compound
Solvent
Chemical shift/ppm
4
5
8
Chloroform-d
Chloroform-d
Chloroform-d
DMSO-d6
−39.0, −36.6
−39.2, −36.6
−40.0, −32.3
−104.4, −41.1
−105.2, −37.5
−105.2, −37.5
2.6
Computational study on the
|
fluxional behavior
[Li(thf)]+6−
[Li(thf)]+7−
DMSO-d6
DMSO-d6
In order to get insights into the observed fluxional behavior
of [Li(crypt-222)]+7−, the computational study of 6− was car-
ried out at the B3PW91 + D3/6-31 + G(d) level of theory.
A transition state (6TS−) that connects two rotamers of 6−
(6a− and 6b−) was found, which was confirmed by the IRC
analysis (vide infra). This process represents a 120° rotation
of the bidentate ligand around the Si-Si axis as shown in an
animated GIF file (IRC_trace.gif, Supporting Information) and
illustrated in Figure 9. We also calculated an alkoxide (6t−)
that has tetracoordinate silicon and can be generated by the
heterolytic cleavage of the Si–O bond. The intervention of
6t− in the fluxional behavior would be unlikely because 6t−
is much higher in energy by 251.7 kJ/mol from 6a− and by
197.2 kJ/mol from transition state 6TS−. The calculated activa-
tion barrier from 6a− to 6b− via 6t− (ΔG‡ = 54.5 kJ/mol) at
298.15 K is in accord with the experimentally obtained value
(ΔG‡ = 43.1 2.1 kJ/mol) at the same temperature.
[Li(crypt-222)]+7−
tetracoordinate silicon atoms in the compounds resonate in
the range of −36.6 to −41.1 ppm. The signals observed at
−104.4 for 6− and −105.2 ppm for 7− in DMSO-d6 can be
assigned to the five-coordinate silicon nuclei because typi-
cal five-coordinate silicon nuclei exhibit signals at these
regions.[1,20] These results are consistent with the five-
coordinate silicate structures of 6− and 7− in DMSO-d6.
Noticeably, the obtained silicates exhibited fluxional be-
havior. As shown in Figure 7, 13C{1H} NMR spectrum of
[Li(crypt-222)]+7− in DMSO-d6 showed six signals due to
the three blades of the 9,10-disilatriptycene moiety at 300 K,
which indicates that two equatorial and one apical blades of
9,10-disilatriptycene exchange their positions on the NMR
timescale. Similar 13C{1H} NMR signal patterns of [Li(thf)]+6−
and [Li(thf)]+7− were obtained in DMSO-d6. Then, we focused
Couzijn and Lammertsma[8] have proposed that dynam-
ics of trigonal bipyramidal five-coordinate compounds can
FIGURE 7 Aromatic region 13C{1H}
spectrum of [Li(crypt-222)]+7− in DMSO-
d6 at 300 K (♦ = signals of residual
toluene). Blue solid and open circles denote
the signals of the 9,10-disilatriptycene and
alkoxyphenyl moieties, respectively

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ISHIDA et Al.
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be interpreted as a single BPR or a combination of BPRs
and each BPR connects two trigonal bipyramidal structures
via a square pyramidal structure as a transition state or a
nonstationary structure. They introduced the topology pa-
rameter (TP) for validating the mechanism of the stereo-
mutation of the five-coordinate species and discussed the
change in TP respect to the reaction coordinate by IRC
calculation.[21] The obtained double V-shaped profile of
TP (Figure 10) suggests that the 120° rotation of the biden-
tate ligand in 6− consists of two sequential BPRs through
−
two square pyramidal structures. The transition state 6TS
adopts distorted trigonal bipyramidal geometry with oxygen
atom occupied at the apical position. The obtained topolog-
ical profile of the stereomutation of 6− with tridentate and
bidentate ligands is similar to those of silicates with two
bidentate ligands.[8]
3
CONCLUSION
|
Anionic alkoxy(tetraaryl)silicates 6− and 7− having
9,10-disilatriptycene skeleton were synthesized by the re-
actions of 5 with tert-butyllithium, and [Li(crypt-222)]+ 7−
salt was successfully isolated and characterized. In the solid
state structure of [Li(crypt-222)]+ 7−, the five-coordinate
silicon adopts distorted trigonal bipyramid geometry, and
a coordinating oxygen atom is located at the equatorial po-
sition. On the basis of the 29Si NMR spectra, compounds
6− and 7− exist as five-coordinate silicate structures in
DMSO-d6 at room temperature. Temperature dependence
of the NMR spectra demonstrated that three o-phenylene
blades of 7− are chemically equivalent at 300 K, which
indicate dynamic behavior of the five-coordinate silicon
because two blades are located at the equatorial position
and one blade lies at the apical position in the solid struc-
ture. The experimentally obtained kinetic parameters of the
interchange process are matched with the value estimated
FIGURE 8 1H NMR spectra of [Li(crypt-222)]+ 7− at
various temperatures (black) and their line-shape simulations (red)
using the following parameters: δA = 8.373 ppm, Δυ1/2 17.5 Hz,
δB = 7.0556 ppm Δυ1/2 = 15.0 Hz
6t−
(251.7)
O
H
Si
O
Si
H
Si
Si
6a−
(0.0)
6b−
(-0.4)
−
6TS
(54.5)
FIGURE 9 Schematic representation
of isomerization path of 6a− and 6b− via
6TS− with 6t− predicted at the B3PW91-
O
Si
O
Si
D3/6-31 + G(d) level of theory. The values
H
H
Si
Si
in parentheses are the free energies or the
activation free energy relative to 6a at
298.15 K in kJ mol−1

ISHIDA et Al.
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4.2.1
Improved synthesis of bis(2-
|
bromophenyl)silane 2
In a three-necked flask equipped with a magnetic stir bar,
1,2-dibromobenzene (65.9 g, 279 mmol) was added to the solu-
tion of iPrMgBr·LiCl in THF (0.75 mol/L, 310 mL) at −25°C,
and thus, obtained solution was stirred for 2.5 hours. Then,
THF solution (56 mL) of dichlorosilane (14.0 g, 139 mmol)
was added to the reaction mixture at −80°C, and the reaction
mixture was stirred for 1 hour. The resulting solution was hy-
drolyzed with saturated aqueous NH4Cl and then extracted
with ether. The combined organic layer was washed with
brine, dried over anhydrous MgSO4, and evaporated to afford
a crude product. The crude product was purified by Kugelrohr
distillation (60°C, 1.5 Pa), and the distillate was washed with
methanol. Pure product was obtained as a colorless solid in
75% yield (71.6 g, 209 mmol). The spectroscopic data of the
product were identical to those in the previous report.[12]
FIGURE 10 IRC trace with TP of the isomerization of 6a− to
6b− via 6TS−. Blue line = IRC trace, red line = TP value
theoretically. Computational study suggested that the ob-
served stereomutation proceeds via a 120° rotation of the
bidentate ligand around the Si-Si axis that consists of two
sequential BPRs.
4
EXPERIMENTAL
General procedures
|
4.2.2
9-(2-Formylphenyl)-9,10-
4.1
|
|
disilatriptycene (4)
All synthetic experiments were performed under argon
In a triple-necked flask equipped with a magnetic stir bar and
a reflux condenser, THF (20 mL) was added to the mixture
of magnesium turnings (802 mg, 33.0 mmol) and 2 (4.80 g,
14.0 mmol) at room temperature and the reaction mixture was
stirredfor10 hourswithreflux. Then, DMF(12 mL, 156 mmol)
was added dropwise to the reaction mixture at 0°C for 1 hour.
The resulting solution was hydrolyzed with saturated aqueous
NH4Cl and was extracted with ether. The combined organic
layer was washed with brine, dried over anhydrous Na2SO4,
and evaporated to afford crude 4. Pure 4 was obtained by
silica-gel column chromatography (eluent:hexane/CHCl3 5:1)
as a colorless solid in 18% yield (491 mg, 1.26 mmol).
or nitrogen in a standard vacuum system unless otherwise
noted. H (400 MHz), 13C{1H} (100 MHz), and 29Si{1H}
1
(79 MHz) NMR spectra of products were recorded on a
1
Bruker Avance 400 FT NMR spectrometer. H (500 MHz),
13C{1H} (125 MHz), and 29Si{1H} (100 MHz) NMR spectra
of products were recorded on a Bruker Ascent 500FT NMR
spectrometer. Sampling of air-sensitive materials was car-
ried out using a VAC Nexus 100027-type glove box. Mass
spectra were obtained on a JEOL JMS-600W mass spec-
trometer. UV-vis spectra and emission spectra were recorded
on a JASCO V-660 and a Hitachi F-4500 spectrometers,
respectively.
1
4: a colorless solid; mp 257-258°C; H NMR (chloro-
form-d, 400 MHz, 297 K) δ 5.61 (s, 1JSi–H = 220 Hz, 1H, SiH),
7.18-7.25 (m, 6H), 7.64 (d, J = 6.8 Hz, 3H), 7.86-7.89 (m,
4H), 7.94 (dt, J = 7.6, 1.6 Hz, 1H), 8.35 (d, J = 7.6 Hz, 1H),
8.75 (d, J = 7.2 Hz, 1H), 10.15 (s, 1H, CHO); 13C{1H}NMR
(chloroform-d, 100 MHz, 298 K) δ 127.7 (CH), 127.9 (CH),
129.3 (CH), 131.6 (CH and C, overlapping), 133.0 (CH), 133.3
(CH), 133.9 (CH), 137.7 (CH), 143.1 (C), 144.25 (C), 144.32
(C), 192.5 (CHO); 29Si{1H} NMR (chloroform-d, 79.5 MHz,
298 K) δ −39.0 (SiAr), −36.6 (SiH); IR (KBr, cm−1) 3039
(υC–H), 2191 (υSi–H), 1700 (υC=O), 1429; MS (EI, 70 eV) 390
(12, M+), 345 (4), 312 (2), 268 (8), 92 (100); Anal. Calcd for
C25H18OSi2: C, 76.88; H, 4.65. Found: C, 76.74, H, 4.73.
4.2
Materials
|
All solvents treating air-sensitive compounds were dried
prior to use. THF was dried over potassium mirror and then
distilled prior to use by using a vacuum line. DMF was dried
over CaH2 and filtered off, then distilled under reduced
pressure. Thus, obtained DMF was stored in the presence
of molecular sieves 4A. Toluene was dried over lithium
aluminum hydride and then distilled prior to use. THF-d8
and DMSO-d6 were dried over molecular sieves 4A and de-
gassed prior to use by using a vacuum line. Other solvents
(dry ether, ethyl acetate, chloroform and chloroform-d,
and hexane) were used as received without further purifi-
cation. 1,2-Dibromobenzene, 2-bromopropane, anhydrous
LiCl, magnesium turnings, dichlorosilane, LiAlH4, tert-
butyllithium, and [2.2.2]cryptand were used as received.
2-bromophenylmagnesium bromide was prepared accord-
ing to the reported method.[22]
4.2.3
9-(2-Hydroxymethylphenyl)-9,10-
|
disilatriptycene 5
In a Schlenk tube equipped with a magnetic stir bar, a suspen-
sion of 4 (1.08 g, 2.77 mmol) in ether (59 mL) was added to

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ISHIDA et Al.
|
a suspension of LiAlH4 (55 mg, 1.45 mmol) in ether (29 mL)
at 0°C. After stirred for 40 minutes, the reaction mixture was
hydrolyzed with saturated aqueous NH4Cl. The resulting so-
lution was extracted with ether. The combined organic layer
was washed with brine, dried over anhydrous Na2SO4, and
evaporated to afford crude 5. Pure 5 was obtained by silica-
gel column chromatography (eluent:hexane/AcOEt 3:1) as a
colorless solid in 83% yield (901 mg, 2.30 mmol).
of the volatiles, the resulting mixture was washed with
dry hexane, and then, the solvent was evaporated. The salt
[Li(thf)]+7− was obtained as a colorless solid in 82% yield
(56 mg, 107 μmol). As compound [Li(thf)]+7− gradually de-
composed even in the solid state, elemental analysis was not
conducted.
[Li(thf)]+[7]−: a colorless solid; mp 264-265°C (decom-
1
posed); H NMR (DMSO-d6, 400 MHz, 298 K) δ 1.72 (s,
1
5: a colorless solid; mp 213-214°C; H NMR (chloro-
9H), 1.73-1.1.80 (m, 4H), 3.58-3.63 (m, 4H), 4.88 (s, 2H,
CH2), 6.30 (d, J = 7.2 Hz, 1H), 6.66 (t, J = 7.2 Hz, 1H), 6.77-
6.79 (m, 6H), 6.95 (t, J = 7.2 Hz, 1H), 7.04 (d, J = 7.2 Hz,
1H), 7.38 (brs, 3H), 7.62-7.65 (m, 3H); 13C{1H}NMR
(DMSO-d6, 100 MHz, 300 K) δ 16.6 (C), 25.1 (CH2, THF),
29.0 (CH3), 63.6 (CH2), 67.0 (CH2, THF), 120.1 (CH), 121.9
(CH), 123.7 (CH), 124.3 (CH), 124.4 (CH), 130.0 (CH),
135.0 (CH), 135.6 (CH), 144.4 (C), 149.4 (C), 154.2 (C),
168.0 (C); 29Si{1H} NMR (DMSO-d6, 79.5 MHz, 299 K) δ
−37.5 (Sit-Bu), −105.2 (Si).
form-d, 400 MHz, 300 K) δ 1.65 (t, J = 5.2 Hz, 1H, OH),
4.73 (d, J = 5.2 Hz, 2H, CH2), 5.59 (s, 1JSi–H = 219 Hz, 1H,
Si–H), 7.19-7.25 (m, 6H), 7.61 (t, J = 7.6 Hz, 1H), 7.68-
7.73 (m, 3H), 7.76 (t, J = 6.8 Hz, 1H), 7.83-7.87 (m, 3H),
7.92 (d, J = 7.6 Hz, 1H), 8.55 (d, J = 6.8 Hz, 1H); 13C{1H}
NMR (chloroform-d, 100 MHz, 300 K) δ 65.5 (CH2), 126.0
(C), 127.5 (CH), 127.7 (CH), 127.8 (CH), 129.2 (CH), 131.7
(CH), 133.0 (CH), 133.3 (CH), 136.7 (CH), 144.4 (C), 144.8
(C), 148.8 (C); 29Si{1H} NMR (chloroform-d, 79.5 MHz,
299 K) δ −39.1 (SiAr), −36.6 (SiH); IR (KBr, cm−1) 3579
(υO–H), 3039 (υC–H), 2168 (υSi–H), 1422; MS (EI, 70 eV) 391
(31, M+ − 1), 314 (8), 269 (9), 92 (100); Anal. Calcd for
C25H20OSi2: C, 76.48; H, 5.13. Found: C, 76.52, H, 5.39.
4.2.6
[Li(crypt-222)]+7−
|
In a Schlenk tube equipped with a magnetic stir bar, a tolu-
ene solution (1 mL) of crypt-222 (107 mg, 284 μmol) was
added dropwise to a toluene solution (1 mL) of silicate
[Li(thf)]+7− (148 mg, 281 μmol) at room temperature and
stirred for 1 day. Colorless solid was precipitated. The pre-
cipitate was washed with dry hexane, and then, the solvent
was evaporated. Compound [Li(crypt-222)]+7− was obtained
as a colorless solid in 82% yield (192 mg, 230 μmol).
4.2.4
[Li(thf)]+6−
|
In a Schlenk tube equipped with a magnetic stir bar, a pen-
tane solution of tert-butyllithium (1.39 mol/L, 0.37 mL) was
added dropwise to a THF solution (1 mL) of 5 (200 mg,
510 μmol) at −78°C and the resulting solution was stirred
for 1 hour. After removal of the volatiles, the reaction mix-
ture was washed with dry hexane, and then, the solvent was
evaporated. The salt [Li(thf)]+6− was obtained as a color-
less solid in 80% yield (192 mg, 408 μmol). As compound
[Li(thf)]+6− gradually decomposed even in the solid state,
elemental analysis was not conducted.
[Li(crypt-222)]+7−: a colorless solid; mp 178-180°C
1
(decomposed); H NMR (DMSO-d6, 500 MHz, 300 K) δ
1.73 (s, 9H, t-Bu), 2.55 (s, 12H, crypt-222), 3.50 (s, 12H,
crypt-222), 3.56 (s, 12H, crypt-222), 4.89 (s, 2H, CH2), 6.32
(d, J = 7.0 Hz, 1H), 6.67 (t, J = 7.0 Hz, 1H), 6.79 (brs, 6H),
6.96 (t, J = 7.0 Hz, 1H), 7.05 (d, J = 7.0 Hz, 1H), 7.39 (brs,
3H), 7.65 (brs, 3H); 13C{1H}NMR (DMSO-d6, 126 MHz,
300 K) δ 16.7 (C), 29.0 (CH3), 55.7 (CH2, crypt-222), 63.6
(CH2), 69.3 (CH2, crypt-222), 70.1 (CH2, crypt-222), 120.1
(CH), 122.0 (CH), 123.7 (CH), 124.3 (CH), 124.4 (CH),
130.0 (CH), 135.0 (CH), 135.7 (CH), 144.4 (C), 149.4 (C),
154.3 (C), 168.1 (C); 29Si{1H} NMR (DMSO-d6, 99.4 MHz,
300 K) δ −37.5 (Sit-Bu), −105.2 (Si); Anal. Calcd for
C47H63LiN2O7Si2: C, 67.92; H, 7.64. Found: C, 67.77, H,
7.57.
[Li(thf)]+6−: a colorless solid; mp 195°C (decomposed);
1H NMR (DMSO-d6, 400 MHz, 297 K) δ 1.73-1.80 (m, 4H),
3.55-3.64 (m, 4H), 4.91 (s, 2H, CH2), 5.14 (s, 1H, SiH), 6.41
(d, J = 7.0 Hz, 1H), 6.72 (t, J = 7.0 Hz, 1H), 6.80-6.87 (m,
6H), 7.00 (t, J = 7.0 Hz, 1H), 7.08 (d, J = 7.0 Hz, 1H), 7.38
(d, J = 6.4 Hz, 3H), 7.45 (d, J = 6.4 Hz, 3H); 13C{1H}NMR
(DMSO-d6, 100 MHz, 298 K) δ 25.2 (CH2, THF), 63.7 (CH2),
67.0 (CH2, THF), 120.2 (CH), 122.6 (CH), 123.9 (CH), 124.5
(CH), 125.4 (CH), 130.4 (CH), 134.9 (CH), 135.4 (CH),
144.8 (C), 149.5 (C), 153.4 (C), 166.1 (C); 29Si{1H} NMR
(DMSO-d6, 79.5 MHz, 297 K) δ −41.1 (SiH), −104.4 (Si).
4.2.7
9-tert-Butyl-10-(2-
|
hydroxymethylphenyl)-9,10-disilatriptycene 8
4.2.5
[Li(thf)]+7−
|
In a Schlenk tube equipped with a magnetic stir bar, a
solution of silicate [Li(thf)]+7− (204 mg, 387 μmol) in
THF (2 mL) was reacted with saturated aqueous NH4Cl
(1 mL) at room temperature for 20 minutes. Then, the re-
action mixture was extracted with ether, and the combined
In a Schlenk tube equipped with a magnetic stir bar, a pen-
tane solution of tert-butyllithium (1.39 mol/L, 0.21 mL) was
added dropwise to a THF solution (0.2 mL) of 5 (51 mg,
130 μmol) at −78°C and stirred for 1 hour. After removal

ISHIDA et Al.
9 of 11
|
organic layer was washed with brine, dried over anhy-
drous Na2SO4, and evaporated to afford crude 8. Pure
8 was obtained by silica-gel column chromatography
(eluent:hexane/AcOEt 3:1) as a colorless solid in 62%
yield (108 mg, 240 μmol).
Crystal data for
5
(CCDC-1864983) (100 K):
0.30 mm × 0.03 mm × 0.03 mm; C25H20OSi2; Formula
weight 392.59; monoclinic; space group Cc (#9);
a = 10.908(3) Å,
b = 20.750(5) Å,
c = 8.759(2) Å,
β = 100.650(3)°,V = 1948.5(8) Å3,Z = 4,Dcalcd = 1.338 Mg/
m3, 2833 reflections measured, 2833 unique (Rint = 0.0311),
which were used in all calculations; R1 = 0.0391 (I > 2σ(I)),
wR2 = 0.1141 (all data), GOF = 1.059, max/min residual
electron densities 0.460/−0.325 e Å−3.
1
8: a colorless solid; mp 201-204°C (decomposed); H
NMR (chloroform-d, 500 MHz, 299 K) δ 1.62 (t, J = 5.0 Hz,
1H, OH), 1.84 (s, 9H, t-Bu), 4.68 (d, J = 5.0 Hz, 2H, CH2),
7.16-7.25 (m, 6H), 7.61 (dt, J = 7.5, 1.0 Hz, 1H), 7.72 (dd,
J = 7.0, 0.5 Hz, 3H), 7.75 (dt, J = 7.5, 1.0 Hz, 1H), 7.92 (d,
J = 7.5 Hz, 1H), 8.02 (dd, J = 7.0, 0.5 Hz, 3H), 8.56 (dd,
J = 7.5, 1.0 Hz, 1H); 13C{1H}NMR (chloroform-d, 126 MHz,
300 K) δ 17.3 (C), 28.9 (CH3), 65.6 (CH2), 126.3 (C), 127.08
(CH), 127.10 (CH), 127.8 (CH), 129.3 (CH), 131.6 (CH),
133.2 (CH), 133.3 (CH), 136.7 (CH), 144.6 (C), 146.5 (C),
149.0 (C); 29Si{1H} NMR (chloroform-d, 99.4 MHz, 299 K)
δ −32.3 (Sit-Bu), −40.0 (Si); IR (KBr, cm−1) 3579 (υO–H),
3041 (υC–H), 1430; MS (EI, 70 eV) 447 (4, [M − H]+), 391
(100), 374 (3), 283 (2), 239 (11), 211 (9), 181 (18), 105 (13);
Anal. Calcd for C29H28OSi2: C, 77.63; H, 6.29. Found: C,
77.60, H, 6.32.
Crystal data for [Li(crypt-222)]+7− (CCDC-1 864 985)
(100 K): 0.20 mm × 0.10 mm × 0.05 mm; C47H63LiN2O7Si2;
Formula weight 831.11; triclinic; space group P-1 (#2);
a = 11.7509(13) Å, b = 12.5126(13) Å, c = 16.5442(18) Å,
α = 83.5840(10)°, β = 87.9320(10)°, γ = 65.7070(10)°,
V = 2203.2(4) Å3, Z = 2, Dcalcd = 1.253 Mg/m3, 11 656
reflections measured, 8847 unique (Rint = 0.0263), which
were used in all calculations; R1 = 0.0460 (I > 2σ(I)),
wR2 = 0.1246 (all data), GOF = 1.025, max/min residual
electron densities 0.552/−0.439 e Å−3.
Crystal data for
8
(CCDC-1864984) (100 K):
0.40 mm × 0.05 mm × 0.04 mm; C29H28OSi2; Formula
weight 448.69; monoclinic; space group P21/n (#14);
a = 12.9056(10) Å, b = 11.4774(8) Å, c = 16.5672(12) Å,
β = 107.7400(10)°, V = 2337.3(3) Å3, Z = 4, Dcalcd = 1.275
Mg m−3, 11 931 reflections measured, 4574 unique
(Rint = 0.0217), which were used in all calculations;
R1 = 0.0377 (I > 2σ(I)), wR2 = 0.0980 (all data),
GOF = 1.022, max/min residual electron densities
0.578/−0.257 e Å−3.
4.3
X-ray analysis
|
Compounds 4, 5, and 8 were recrystallized by slow cool-
ing of the toluene solution from 90°C to room tempera-
ture to grow single crystals suitable for XRD analysis.
Single crystals of [Li(crypt-222)]+7− were obtained by a
slow diffusion method; toluene solution of crypt-222 was
put on toluene solution of [Li(thf)]+7− at room tempera-
ture. The single crystals coated by Apiezon® grease were
mounted on a thin glass fiber and transferred to the cold
nitrogen gas stream of the diffractometer. X-ray data were
collected on a Bruker AXS APEX II CCD diffractometer
with graphite monochromated Mo-Kα radiation. An em-
pirical absorption correction based on the multiple meas-
urement of equivalent reflections was applied using the
program SADABS.[23] Structures were solved by direct
methods and refined by full-matrix least squares against F2
using all data (SHELXL-2014[24] and Yadokari-XG soft-
ware[25]). The supplementary crystallographic data for this
paper (CCDC-1864982 to 1864985) can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_cif.
4.4
Theoretical study
|
All theoretical calculations were performed using
a
Gaussian 09[26] and GRRM 14[27] programs. Geometrical
optimization and frequency analysis were carried out at the
B3PW91 + D3/6-31 + G(d) level of theory. Initially, the
optimized structures of two rotamers of 6− (6a− and 6b−)
−
are calculated; then, the transition state 6TS that connects
6a− and 6b− was computed using 2PSHS method.[28] No
imaginary frequencies were found in the equilibrium struc-
tures of 6a−, 6b−, and 6t−, whereas one imaginary frequency
was found in a transition state (6TS−). Atomic coordinates of
the optimized structures of the compounds with energy with
zero-point correction are summarized in Tables S1-S4 in the
Supporting Information. The reaction path from 6a− to 6b−
via 6TS− was confirmed by IRC calculation.[29] An animated
GIF file (IRC_trace.gif) that represents the above IRC trace
was prepared using ChemCraft.[30]
Crystal data for
4
(CCDC-1864982) (100 K):
0.20 mm × 0.20 mm × 0.05 mm; C25H18OSi2; Formula
weight 390.57; monoclinic; space group P21/n (#14);
a = 11.175(2) Å,
b = 12.536(2) Å,
c = 13.678(3) Å,
β = 92.419(2)°, V = 1914.6(6) Å3, Z = 4, Dcalcd = 1.355 Mg/
m3, 9555 reflections measured, 3748 unique (Rint = 0.0488),
which were used in all calculations; R1 = 0.0489 (I > 2σ(I)),
wR2 = 0.1349 (all data), GOF = 1.030, max/min residual
electron densities 0.713/−0.629 e Å−3.
ACKNOWLEDGMENTS
This work was supported by the Cooperative Research
Program of “Network Joint Research Center for Materials

10 of 11
ISHIDA et Al.
|
and Devices” (S.I.), JSPS KAKENHI [Nos. JP25708004 and
JP25620020 (S.I.)].
2009, 131, 3741; e) L. J. P. van der Boon, L. van Gelderen, T. R.
de Groot, M. Lutz, J. C. Slootweg, A. W. Ehlers, K. Lammertsma,
Inorg. Chem. 2018, 57, 12697.
[10] Related constraint five-coordinate phosphorous compounds, see:
a) P. Gillespie, P. Hoffman, H. Klusacek, D. Marquarding, S.
Pfohl, F. Ramirez, E. A. Tsolis, I. Ugi, Angew. Chem. Int. Ed.
Engl. 1971, 10, 687; b) F. Ramirez, I. Ugi, F. Lin, S. Pfohl, P.
Hoffman, D. Marquarding, Tetrahedron 1974, 30, 371; c) F.
Ramirez, Y. F. Chaw, J. F. Marecek, I. Ugi, J. Am. Chem. Soc.
1974, 96, 2429.
ORCID
Shintaro Ishida
https://orcid.org/0000-0001-7832-912X
https://orcid.org/0000-0002-8556-5785
Takeaki Iwamoto
[11] S. Matsukawa, H. Yamamichi, Y. Yamamoto, K. Ando, J. Am.
Chem. Soc. 2009, 131, 3418.
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SUPPORTING INFORMATION
Additional supporting information may be found online in
the Supporting Information section at the end of the article.
How to cite this article: Ishida S, Takiguchi M,
Iwamoto T. Alkoxy(tetraaryl)silicates bearing
9,10-disilatriptycene skeleton. Heteroatom Chem.
2018;e21481. https://doi.org/10.1002/hc.21481
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