2,3,5,6,7,8-Hexasilabicyclo[2.2.2]octane-1-carboxylic acids and esters: Preparation and structure

Article abstract of DOI:10.1016/S0022-328X(03)00161-X

Polysilacage acid HC(SiMe₂SiMe₂)₃ CCO₂H was prepared quantitatively by deprotonation of HC(SiMe₂SiMe₂)₃CH by a superbase in excess followed by trapping with CO₂. The a

Full text of DOI:10.1016/S0022-328X(03)00161-X

Journal of Organometallic Chemistry 685 (2003) 138ꢀ144
/
www.elsevier.com/locate/jorganchem
2,3,5,6,7,8-Hexasilabicyclo[2.2.2]octane-1-carboxylic acids and esters:
preparation and structure
Masaki Shimizu *, Susumu Sugimoto, Hirofumi Mizukoshi, Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Received 27 December 2002; received in revised form 7 March 2003; accepted 10 March 2003
Abstract
Polysilacage acid HC(SiMe2SiMe2)3CCO2H was prepared quantitatively by deprotonation of HC(SiMe2SiMe2)3CH by a
superbase in excess followed by trapping with CO2. The acid allowed to disclose X-ray analysis of hydrogen-bonded dimers that
preferred pairs of the same enantiomeric isomers. Cage diacid HO2CC(SiMe2SiMe2)3CCO2H also was prepared. Esterification of
the acids was found to proceed in good yields via the Mitsunobu conditions using diisopropyl azodicarboxylate.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Bicyclo[2.2.2]octane; Cage compound; Cage acid; Cage ester; Mitsunobu reaction; Silicon
1. Introduction
work can induce novel and unique properties of the
resulting compounds.
In general, a bicyclo[2.2.2]octane moiety incorporated
in an organic molecule induces molecular rigidity and
enhances thermal stability. Therefore, such a bicyclic
ring is often utilized as a mesogen of calamitic liquid
crystalline compounds as well as molecular rods [1].
We have recently established an efficient route to
2,2,3,3,5,5,6,6,7,7,8,8-docecamethyl-2,3,5,6,7,8-hexasila-
bicyclo[2.2.2]octane (1, Fig. 1) [2]. Functionalization of
the polysilacage compound can be effected by metala-
tion at the bridgehead position with a superbase
consisting of BuLi and t-BuOK and subsequent reaction
with such an electrophile as chlorosilane, chlorostan-
nane, alkyl halide, bromine, iodine, or diphenyldisulfide
[2a]. In particular, cyclohexenylation at the brigehead
position followed by dehydrogenation allows us to
prepare phenyl-substituted polysilacage molecules [3].
Among functionalized cage compounds, 1-pentyl-4-
phenyl derivative 2 was found to exhibit tree texture
characteristic to discotic hexagonal phase, inspite of the
rod-like shape of 2. This observation clearly indicates
that substitution of carbons with silicons in cage frame-
In order to extend the possibility of novel liquid
crystalline compounds based on 2,3,5,6,7,8-hexasilabi-
cyclo[2.2.2]octane, we turned our attention to polysila-
cage (di)acids and (di)esters 3ꢀ6, because carboxylic
/
acids can be liquid crystals by forming hydrogen-bonded
dimers and ester functionality is often utilized as a
linking group in liquid crystals. Hence, development of
preparative routes to polysilacage acids and esters and
structural examination of the cage acids are crucial for
further exploration of novel materials based on the cage
acid derivatives. Here, we report the preparation and
structure of the cage acids and esterification.
2. Results and discussion
2.1. Preparation and structure of polysilacage acid 3
Treatment of 1 (1 mol) with BuLi (4 mol) and t-
BuOK (4 mol) in THF at ꢁ42 8C followed by bubbling
/
of CO2 gas gave 2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane-
1-carboxylic acid 3 as a colorless solid (dec. 165 8C) in
99% yield (Eq. 1). Diacid 4 was not produced at all
despite the presence of a superbase in excess [2a].
* Corresponding author. Tel.: ꢂ
5555.
E-mail address: shimizu@npc05.kuic.kyoto-u.ac.jp (M. Shimizu).
/
81-75-753-5535; fax: ꢂ81-75-753-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00161-X

M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ
/
144
139
Fig. 1. SiꢃSiMe2.
/
ð1Þ
The carbonyl stretching absorption of 3 in infrared
(IR) spectroscopy appeared at 1640 cmꢁ1. Since the
absorptions of most alkanoic acids range from 1700 to
1730 cmꢁ1 and conjugation is known to move the
absorption to a lower frequency [4], sꢀp conjugation
/
between the cage moiety and the carbonyl group in 3 is
clearly demonstrated.
Cage acid 3 crystallized from hexane in the mono-
clinic space group C2/c [5]. In the solid state, the
molecule was axially chiral because hexasilabicy-
clo[2.2.2]octane framework was distorted from an ideal
conformation of bicyclo[2.2.2]octane in a right- or left-
handed manner. The left-handed molecular structure of
3 is shown in Fig. 2. The carboxyl carbonyl and one of
silicon-bridgehead carbon bonds formed to be eclipsed.
Fig. 3. Packing diagram of 3 (Mꢃ
/
right-handed 3, Pꢃ
/
left-handed 3).
˚
layers that were 17.89 A thick and alternatively stacked
in a single crystal.
Dihedral angles of SiÃ
/
C(1)Ã
/
C(4)Ã/Si ranged from 16.9
to 19.68 which were larger than those of 1 (128),
indicating that introduction of a carboxyl group at a
bridgehead position made the hexasilabicyclo[2.2.2]oc-
tane framework more distorted.
Packing diagram of 3 is shown in Fig. 3. Each chiral
molecule was hydrogen-bonded with the same enantio-
mer to form dimers. In other words, a right-handed
molecule dimerized with a right-handed one, while a
left-handed one was self-assembled with a left-handed
enantiomer. Two kinds of dimers, respectively, made
2.2. Preparation of polysilacage diacid 4
Preparation of diacid 4 was also studied. Direct
carboxylation of 3 initially attempted by treatment of
3 with the superbase and then CO2 gas resulted in the
decomposition of 3. Therefore, we examined an indirect
route to 4 (Scheme 1). Thus, 1 was firstly converted into
phenylthio derivative 7 by treatment with the superbase
and then with PhSSO2Ph [6] in 69% yield. The sequence
of metalation and carboxylation gave acid 8 in 69%
Fig. 2. Molecular structure of left-handed 3.

140
M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ
/
144
Scheme 1.
yield. Finally, a lithium salt of 8 generated by treatment
with BuLi in THF was reduced with lithium 4,4?-di(tert-
butyl)biphenylide [7] and carboxylated with CO2 gas to
produce 4 in 78% yield as a solid material. Although
recrystallization of 4 was attempted in various ways, no
single crystals suitable for X-ray analysis were obtained.
work of 3. Then, we envisaged that use of bulkier dialkyl
azodicarboxylate would retard such undesirable process.
Actually, yields of esters 5 increased simply by switching
dimethyl azodicarboxylate to diisopropyl azodicarbox-
ylate as demonstrated in Table 1. Thus, esters 5c, 5d and
5g were isolated in slightly enhanced yields (59, 69 and
82%, respectively), while propargylic ester 5e and alkyl
ester 5f were produced in considerably improved yields
(92 and 78%).
2.3. Esterification of polysilacage acids 3 and 4 under
Mitsunobu conditions
Propargylic ester 5e decomposed upon heating (de-
composition point 76 8C) while alkyl and 2-alkenyl
esters 5 were thermally stable (m.p.: 5a, 180 8C; 5b,
With cage (di)acids 3 and 4 in hand, we next
scrutinized their esterification. Cage acid 3 reacted
with Me3SiCHN2 in benzene/methanol at room tem-
perature to give methyl ester 5a in 93% yield (Eq. 2),
while condensation with methanol in the presence of
oxalyl chloride or isobutyl chloroformate, or with
phenol using dicyclohexylcarbodiimide as a dehydrating
agent resulted in the decomposition of the polysilacage
moiety to yield a complex mixture.
97 8C; 5c, 106 8C; 5d, 134 8C; 5f, 73.5ꢀ74.6 8C; 5g,
/
131 8C). No alkyl and 2-alkenyl esters, however, ex-
hibited liquid crystallinity presumably because most of
rod-like liquid crystals consisted of two or more rings.
Hence, introduction of ring moieties into polysilacage
esters is considered to be rational for further exploration
of liquid crystals based on the cage acid derivatives.
3. Experimental
ð2Þ
All temperatures were not corrected. Melting points
were determined using a YANAKO MP-500D appara-
tus. All manipulations of oxygen- and moisture-sensitive
materials were conducted with the standard Schlenk
technique under a purified argon atmosphere (deoxyge-
nated by passing through BASF-Catalyst R3-11 column
These results indicate that nucleophilic attack at the
carbonyl carbon in 3 is quite difficult to proceed
probably due to severe steric hindrance at the bridge-
head position surrounded by three SiMe2 groups. On the
other hand, nucleophilic reaction of the carboxyl oxygen
is possible. Treatment of 3 or 4 with cyclohex-2-ene-1-ol
in the presence of triphenylphosphine and dimethyl
azodicarboxylate [8] in THF gave ester 5b or 6b in 89
or 94% yield, respectively, after purification using gel
permeation chromatography (GPC) (Table 1 and Eq. 3).
However, esterification with such alcohols as (E)- or
(Z)-pent-2-en-1-ol, dodec-2-yn-1-ol, octan-1-ol, and
(S)-1-phenylethanol under the same conditions afforded
the corresponding products less efficiently as shown in
Table 1. Since consumption of acid 3 and decomposition
of the polysilacage framework were observed by 1H-
NMR of the crude products, a betaine intermediate
generated from triphenylphosphine and dimethyl azodi-
carboxylate might attack silicons and cleave the frame-
1
at 80 8C). H-NMR spectra were measured on a Varian
Mercury 200 (1H, 200 MHz) spectrometer. Chemical
1
shifts of H-NMR are expressed in parts per million
downfield relative to an internal tetramethylsilane (dꢃ
/0
ppm) or chloroform (dꢃ7.26 ppm). Splitting patterns
/
are indicated as s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet; brs, broad singlet. 13C-NMR
spectra were measured on a Varian Mercury 200 (13C,
50 MHz) and JEOL JMN ECP-500 (13C, 125 MHz)
spectrometer with tetramethylsilane as an internal
standard (dꢃ
0 ppm). 29Si-NMR spectra were measured
/
on a JEOL EX-270 (29Si, 54 MHz) or JEOL JMN ECP-
500 (29Si, 99 MHz) spectrometer with tetramethylsilane
as an internal standard (dꢃ0 ppm). IR spectra were
/

M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ
/
144
141
(3)
recorded on a Shimadzu FTIR-8400 spectrometer. GCꢀ
/
carried out using Wakogel C-200. Preparative recycling
MS analyses were obtained with a JEOL JMS-700
spectrometer by electron ionization at 70 eV. FAB-MS
analyses were performed with a JEOL JMS-HX110A
spectrometer using 3-nitrobenzyl alcohol or thiogrycerol
as matrix. Elemental analyses were carried out with a
YANAKO MT2 CHN CORDER machine at Kyoto
University Elemental Analysis Center. TLC analyses
were performed by means of Merck Kieselgel 60 F254
and Rf values were given. Column chromatography was
GPC was performed with a JAI LC-908 chromatograph
equipped with JAIGEL-1H and -2H columns (chloro-
form was used as an eluent). Cooling a reaction vessel at
ꢁ
/
78 and ꢁ40 8C was effected using methanol with dry
/
ice. Ethereal solvents like THF, and diethyl ether were
distilled from benzophenone and sodium under an
argon atmosphere. Butyllithium was purchased from
Sigma-Aldrich Co. Inc. and titrated before use with N-
pivaloyl-o-toluidine as an indicator.

142
M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ144
/
3.1. Synthesis of 2,2,3,3,5,5,6,6,7,7,8,8-dodecamethyl-
2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane-1-carboxylic
acid (3)
3.3. Synthesis of 2,2,3,3,5,5,6,6,7,7,8,8-dodecamethyl-4-
phenylthio-2,3,5,6,7,8-hexasilabicyclo-[2.2.2]octane-1-
carboxylic acid (8)
To a suspension of 1 (75 mg, 0.20 mmol) and t-BuOK
(94 mg, 0.84 mmol) in THF (3.0 ml) was added BuLi
To a suspension of 7 (0.24 g, 0.50 mmol) and t-BuOK
(0.22 g, 2.0 mmol) in THF (8.0 ml) was added BuLi
(1.54 M in hexane, 0.52 ml, 0.80 mmol) at ꢁ
/
42 8C. The
(1.56 M in hexane, 1.3 ml, 2.0 mmol) at ꢁ
/
42 8C. The
reaction mixture was stirred for 1 h at ꢁ42 8C and then
/
reaction mixture was stirred for 1 h at ꢁ42 8C and CO2
/
CO2 gas was bubbled for 1 h before quenching with 1 M
HCl aqueous solution. The aqueous layer was extracted
with ethyl acetate (twice) and chloroform (twice). The
combined organic layer was neutralized with saturated
aqueous NaHCO3 solution, washed with saturated
aqueous NaCl solution, and dried over anhydrous
sodium sulfate. Removal of organic solvent by rotary
evaporator under reduced pressure followed by column
chromatography on silica gel (hexane and then hexane/
ethyl acetate 10:1) afforded 3 (83 mg, 99%).
gas was bubbled for 1 h before quenching with 1 M HCl
aqueous solution. The aqueous layer was extracted with
ethyl acetate twice. The combined organic layer was
washed with saturated aqueous NaCl solution and dried
over anhydrous sodium sulfate. Removal of organic
solvent by rotary evaporator under reduced pressure
followed by column chromatography on silica gel
(hexane/ethyl acetate 4:1) afforded 8 (0.21 g, 78% yield).
1
Colorless solid. M.p.: 175 8C. H-NMR: d 0.27 (s,
Colorless solid. M.p.: 165 8C (dec.). 1H-NMR: d 0.07
18H), 0.31 (s, 18H), 7.20ꢀ
2H). 13C-NMR: d 1.1, 1.8, 18.9, 29.7, 128.4, 129.0,
133.9, 138.6, 180.0. 29Si-NMR: d ꢁ
17.2, ꢁ17.3. IR:
nmax 2986, 2947, 2899, 2361, 1643, 1254, 1220, 978, 814,
685, 658 cmꢁ1. FAB LRMS: m/z 528 [Mꢂꢂ
2], 527
[Mꢂꢂ1], 526 [Mꢂ], 525, 509, 417, 401, 329, 261, 73, 59.
FAB HRMS: Calc. for C21H43O2S1Si6 [Mꢂꢂ
1]:
/
7.33 (m, 3H), 7.73ꢀ
/
7.76 (m,
(s, 1H), 0.23 (s, 18H), 0.31 (s, 18H). 13C-NMR: d 1.7,
3.1, 3.3, 178.8. 29Si-NMR: d ꢁ
3450, 2920, 2824, 1640, 1370, 1250, 1220, 965, 810, 678,
660 cmꢁ1. FAB LRMS: m/z 421[Mꢂꢂ3], 420 [Mꢂꢂ
2], 419 [Mꢂꢂ1], 418 [Mꢂ], 401, 377, 261, 129, 73. FAB
HRMS: Calc. for C15H39O2Si6 [Mꢂꢂ
1]: 419.1566.
Found: 419.1555.
/
19.5, ꢁ21.4. IR: nmax
/
/
/
/
/
/
/
/
/
/
527.1599. Found: 527.1602.
3.2. Synthesis of 1-phenylthio-2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane
(7)
3.4. Synthesis of 2,2,3,3,5,5,6,6,7,7,8,8-dodecamethyl-
2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane-1,4-dicarboxylic
acid (4)
To a suspension of 1 (0.75 g, 2.0 mmol) and t-BuOK
(0.90 g, 8.0 mmol) in THF (20 ml) was added BuLi (1.49
To a solution of 8 (0.54 g, 1.0 mmol) in THF (20 ml)
was added BuLi (1.49 M in hexane, 0.70 ml, 1.0 mmol)
at 0 8C. The resulting solution was stirred for 10 min at
M in hexane, 5.4 ml, 8.0 mmol) at ꢁ
mixture was stirred for 1 h at ꢁ42 8C, treated with a
solution of PhSSO2Ph (3.0 g, 12 mmol) in THF (5.0 ml)
at ꢁ42 8C, and allowed to warm to room temperature.
/
42 8C. The resulting
/
0 8C, cooled to ꢁ78 8C, and treated with lithium 4,4?-di-
/
tert-butylbiphenylide (prepared from lithium dispersion
(30 wt.%, 0.20 g, 29 mmol) and 4,4?-di-tert-butylbiphe-
nyl (2.7 g, 10 mmol) in THF (20 ml)). The reaction
/
Quenching with saturated aqueous NH4Cl solution was
followed by the extraction of aqueous layer with diethyl
ether (twice). The combined organic layer was washed
with saturated aqueous NaCl solution, dried over
anhydrous MgSO4, and concentrated in vacuo. The
crude product was purified by column chromatography
on silica gel (hexane) afforded 7 (0.67 g, 69% yield).
mixture was stirred for 4 h at ꢁ
/
78 8C before bubbling of
CO2 gas for 1 h at ꢁ78 8C. Quenching with 5 M HCl
/
aqueous solution followed by usual workup gave a
crude product, which was purified by column chroma-
tography on silica gel (CHCl3/MeOH 10:1) to produce 4
Colorless solid. M.p.: 208ꢀ
0.13 (s, 1H), 0.20 (s, 18H), 0.24 (s, 18H), 7.24ꢀ
(m, 3H), 7.72ꢀ
7.77 (m, 2H). 13C-NMR: d 1.1, 3.7, 20.2,
128.2, 128.7, 134.6, 138.6. 29Si-NMR: d ꢁ
20.1, ꢁ71.6.
/
210 8C. 1H-NMR: d
7.31
(0.36 g, 78% yield).
1
ꢁ
/
/
Colorless solid. M.p.: ꢀ
/
300 8C. H-NMR (THF-d8):
/
d 0.33 (s, 36H). 13C-NMR (THF-d8): d 2.1, 175.2.
29Si-NMR (THF-d8):
19.7. IR: nmax 2910,
2850, 1640, 1458, 1365, 1250, 1205, 970, 875, 858,
803, 660 cmꢁ1. FAB LRMS: m/z 464 [Mꢂꢂ
2],
463 [Mꢂꢂ1], 462 [Mꢂ], 461 [Mꢂꢁ
1], 445, 73.
FAB HRMS: Calc. for C16H37O4Si6 [Mꢂꢁ
1]:
461.1308. Found: 461.1314.
/
/
d
ꢁ
/
IR: nmax 2982, 2943, 2895, 2831, 1468, 1437, 1253, 970,
810, 752, 708, 679, 653, 590 cmꢁ1. FAB LRMS: m/z 486
/
[Mꢂꢂ
[Mꢂ], 481[Mꢂꢁ
Calc. for C20H42S1Si6: 482.1623. Found: 482.1616.
/
4], 485 [Mꢂꢂ
/
3], 484 [Mꢂꢂ
/
2], 483[Mꢂꢂ
/1], 482
/
/
/
1], 467, 405, 373, 73. FAB HRMS:
/

M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ
/
144
143
3.5. Synthesis of methyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5a)
3.7.2. (Z)-Pent-2-enyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5c)
1
Colorless solid. M.p.: 106 8C. H-NMR: d ꢁ
/
0.09 (s,
7.6
6.9 Hz), 5.50ꢀ
5.62 (m, 1H). 13C-NMR: d 1.8, 3.2,
3.3, 14.1, 20.8, 25.6, 59.8, 123.4, 136.4, 174.2. 29Si-
NMR: d ꢁ20.9, ꢁ19.2. IR: nmax 2951, 2897, 1678,
1437, 1400, 1256, 1161, 1005, 970, 812, 723, 681 cmꢁ1
FAB LRMS: m/z 488 [Mꢂꢂ2], 487 [Mꢂꢂ
1], 486
[Mꢂ], 417, 401, 329, 305, 129, 73. FAB HRMS: Calc.
for C20H47O2Si6 [Mꢂꢂ
1]: 487.2191. Found: 487.2178.
To a suspension of 3 (0.39 mg, 0.93 mmol) in benzene
(8.0 ml) and MeOH (3.0 ml) was added trimethylsilyl-
diazomethane (2 M in hexanes, 2.3 ml, 4.6 mmol) at
room temperature. The reaction mixture was stirred for
1 h at room temperature and quenched with acetic acid.
The resulting mixture was concentrated in vacuo to
afford a crude product. Purification by column chro-
matography on silica gel (hexane/ethyl acetate 5:1) gave
1H), 0.22 (s, 18H), 0.28 (s, 18H), 0.99 (t, 3H, Jꢃ
Hz), 2.03ꢀ2.16 (m, 2H), 4.60 (t, 2H, Jꢃ
5.56 (m, 1H), 5.56ꢀ
/
/
/
/
/
/
/
.
/
/
rise to 5a (0.40 g, 93% yield).
/
1
Colorless solid. M.p.: 180 8C. H-NMR: d ꢁ
/
0.10 (s,
1H), 0.21 (s, 18H), 0.26 (s, 18H), 3.62 (s, 3H). 13C-
3.7.3. (E)-Pent-2-enyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5d)
NMR: d 1.7, 3.2, 3.3, 25.6, 50.9, 174.8. 29Si-NMR: d
ꢁ
/
21.4, ꢁ
1425, 1396, 1256, 1167, 970, 926, 812, 712, 683, 664, 590
cmꢁ1. FAB LRMS: m/z 435 [Mꢂꢂ3], 434 [Mꢂꢂ
2],
433 [Mꢂꢂ
1], 417, 373, 307, 129, 73. FAB HRMS: Calc.
for C16H41O2Si6[Mꢂꢂ
1]: 433.1722. Found: 433.1725.
/
19.7. IR: nmax 2984, 2945, 2897, 2831, 1682,
1
Colorless solid. M.p.: 134 8C. H-NMR: d ꢁ
/
0.09 (s,
7.6
6.9 Hz), 5.54ꢀ
5.84 (m, 1H). 13C-NMR: d 1.8, 3.2,
3.3, 13.3, 25.3, 25.6, 65.1, 123.7, 137.9, 174.1. 29Si-
NMR: d ꢁ20.9, ꢁ19.2. IR: nmax 2925, 2897, 1682, 1458,
1375, 1254, 1167, 968, 812, 681, 665 cmꢁ1. FAB LRMS:
m/z 488 [Mꢂꢂ2], 487 [Mꢂꢂ1], 486 [Mꢂ], 417, 401,
373, 329, 305, 261, 129, 73. FAB HRMS: Calc. for
C20H47O2Si6 [Mꢂꢂ
1]: 487.2191. Found: 487.2204.
/
/
1H), 0.21 (s, 18H), 0.28 (s, 18H), 0.99 (t, 3H, Jꢃ
Hz), 2.00ꢀ2.10 (m, 2H), 4.49 (d, 2H, Jꢃ
5.61 (m, 1H), 5.77ꢀ
/
/
/
/
/
/
/
/
/
3.6. Typical procedure for esterification of cage acid 3
with diisopropyl azodicarboxylate
/
/
/
To a suspension of triphenylphosphine (26 mg, 0.10
mmol) in THF (1.0 ml) was added isopropyl azodicar-
3.7.4. Dodec-2-ynyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5e)
boxylate (20 mg, 0.10 mmol) at ꢁ
mixture was stirred for 10 min at ꢁ
alcohol was added (0.10 mmol) at ꢁ40 8C. The resulting
mixture was stirred for additional 10 min at ꢁ40 8C,
treated with a solution of 3 (0.10 mmol) in THF (1.0
ml), allowed to warm to room temperature gradually,
and filtered through a pad of Florisil. The filtrate was
concentrated in vacuo and purified by GPC to give the
corresponding ester 5.
/
40 8C. The reaction
/
40 8C, and an
/
Colorless solid. M.p.: 76 8C (dec.). 1H-NMR: d
/
ꢁ
/
0.09 (s, 1H), 0.21 (s, 18H), 0.29 (s, 18H), 0.86 (t,
3H, Jꢃ6.4 Hz), 1.20ꢀ1.30 (m, 12H), 1.42ꢀ1.53 (m, 2H),
2.15ꢀ2.20 (m, 2H), 4.60ꢀ
4.65 (m, 2H). 13C-NMR: d 1.7,
3.1, 3.2, 14.1, 18.7, 22.6, 28.4, 28.8, 29.2, 29.3, 29.5, 31.9,
52.0, 74.9, 86.8, 173.5. 29Si-NMR: d ꢁ
21.4, ꢁ19.4. IR:
nmax 2987, 2955, 2361, 1659, 1256, 1196, 970, 876, 810,
667 cmꢁ1. FAB LRMS: m/z 586 [Mꢂꢂ4], 585 [Mꢂꢂ
3], 584 [Mꢂꢂ2], 583 [Mꢂꢂ
1], 567, 525, 489, 455, 261,
129, 73. FAB HRMS: Calc. for C27H59O2Si6 [Mꢂꢂ
1]:
/
/
/
/
/
/
/
/
/
/
/
3.7. Spectral data for cage esters 5
/
583.3130. Found: 583.3134.
3.7.1. Cyclohex-2-enyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5b)
3.7.5. Octyl 2,2,3,3,5,5,6,6,7,7,8,8-dodecamethyl-
2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-1-carboxylate
(5f)
1
Colorless solid. M.p.: 97 8C. H-NMR: d ꢁ
/
0.09 (s,
Colorless solid. M.p.: 73.5ꢀ
0.09 (s, 1H), 0.22 (s, 18H), 0.28 (s, 18H), 0.88 (t,
3H, Jꢃ6.9 Hz), 1.22ꢀ1.40 (m, 10H), 1.60ꢀ1.67 (m, 2H),
4.04 (t, 2H, Jꢃ
6.9 Hz). 13C-NMR: d 1.8, 3.2, 3.3, 14.1,
22.6, 25.6, 26.3, 29.1, 29.20, 29.22, 31.8, 64.5, 174.5. 29Si-
NMR: d ꢁ20.9, ꢁ19.4. IR: nmax 2926, 2855, 1682, 1256,
1169, 812, 681, 665 cmꢁ1. FAB LRMS: m/z 534 [Mꢂꢂ
4], 533 [Mꢂꢂ3], 532 [Mꢂꢂ2], 531 [Mꢂꢂ
1], 515, 417,
329, 129, 73, 57, 43. FAB HRMS: Calc. for C23H55O2Si6
[Mꢂꢂ
1]: 531.2818. Found: 531.2811.
/
74.6 8C. 1H-NMR: d
1H), 0.22 (s, 18H), 0.29 (s, 18H), 1.60ꢀ/1.95 (m, 4H),
ꢁ
/
2.03 (m, 2H), 5.26 (m, 1H), 5.74 (m, 1H), 5.90 (m, 1H).
13C-NMR: d 1.8, 3.1, 3.3, 19.1, 24.8, 25.5, 28.8, 68.1,
/
/
/
/
126.6, 131.6, 173.9. 29Si-NMR: d ꢁ
/
21.3, ꢁ
nmax 2920, 2855, 1674, 1460, 1377, 1254, 1173, 972, 812,
665 cmꢁ1. FAB MS: m/z 501 [Mꢂꢂ3], 500 [Mꢂꢂ
2],
499 [Mꢂꢂ1], 498 [Mꢂ], 418, 402, 330, 129, 73. FAB
/
19.8. IR:
/
/
/
/
/
/
/
/
/
HRMS: Calc. for C21H46O2Si6: 498.2113. Found:
498.2122.
/

144
M. Shimizu et al. / Journal of Organometallic Chemistry 685 (2003) 138ꢀ144
/
3.7.6. (S)-1-Phenylethyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1-carboxylate (5g)
Data Centre, CCDC No. 200 333 for compound 3.
Copies of this information may be obtained free of
charge from: The Director, CCDC, 12 Union Road,
1
Colorless solid. M.p.: 131 8C. H-NMR: d ꢁ
/
0.10 (s,
Cambridge, CB2 1EZ UK (Fax: ꢂ44-1223-336033 or e-
/
1H), 0.2025/0.2071 (split) (s, 18H), 0.24 (s, 18H), 1.58 (d,
3H, Jꢃ6.4 Hz), 5.89 (q, 1H, Jꢃ6.4 Hz), 7.25ꢀ7.29 (m,
1H), 7.30ꢀ7.35 (m, 2H). 7.37ꢀ
7.42 (m, 2H). 13C-NMR:
d 1.75, 1.82, 3.1, 3.20, 3.28, 21.9, 25.5, 72.7, 127.0, 127.8,
128.3, 141.7, 175.5. 29Si-NMR: d ꢁ
20.9, ꢁ19.2. IR:
nmax 2923, 2854, 1672, 1461, 1377, 1253, 1167, 1055, 812
cmꢁ1. FAB LRMS: m/z 525 [Mꢂꢂ3], 524 [Mꢂꢂ
2],
523 [Mꢂꢂ
1], 417, 401, 329, 105, 73. FAB HRMS: Calc.
for C23H47O2Si6 [Mꢂꢂ
1]: 523.2192. Found: 523.2180.
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
/
/
/
/
/
/
/
Acknowledgements
/
/
/
This work was supported by Grant-in-Aids for COE
Research on Elements Science, No. 12CE2005 and
Scientific Research on Priority Areas (A) ‘Exploitation
of Multi-Element Cyclic Molecules’ from Ministry of
Education, Culture, Sports, Science, and Technology,
Japan. The authors thank Prof. Susumu Kitagawa and
Dr Mitsuru Kondo of Kyoto University for X-ray
analysis.
/
3.7.7. Dicylohex-2-enyl 2,2,3,3,5,5,6,6,7,7,8,8-
dodecamethyl-2,3,5,6,7,8-hexasilabicyclo[2.2.2]-octane-
1,4-dicarboxylate (6b)
Colorless solid. M.p.: 157 8C. 1H-NMR: d 0.32 (s,
36H), 1.55ꢀ
5.90 (m, 2H). 13C-NMR: d 1.8 19.1, 24.8, 28.8, 68.3,
126.4, 132.0, 173.6. 29Si-NMR: d ꢁ
18.9. IR: nmax 2928,
2860, 1672, 1394, 1254, 1163, 1022, 870, 812, 669 cmꢁ1
FAB LRMS: m/z 625 [Mꢂꢂ3], 624 [Mꢂꢂ
2], 623
[Mꢂꢂ1], 622 [Mꢂ], 608, 525, 417, 401, 329, 73. FAB
/2.10 (m, 12H), 5,26 (m, 2H), 5.73 (m, 2H),
/
.
/
/
References
/
HRMS: Calc. for C28H54O4Si6: 622.2638. Found:
622.2634.
[1] (a) D. Demus, J. Goodby, G.W. Gray, H.-W. Spiess, V. Vill (Eds.),
Handbook of Liquid Crystals, vols. 1-3, Wiley-VCH, Weinheim,
1998;
(b) P.F.H. Schwab, M.D. Levin, J. Michl, Chem. Rev. 99 (1999)
1863.
4. Summary
[2] (a) M. Shimizu, N. Inamasu, Y. Nishihara, T. Hiyama, Chem.
Lett. (1998) 1145;
(b) M. Shimizu, T. Hiyama, T. Matsubara, T. Yamabe, J.
Organomet. Chem. 611 (2000) 12.
We have demonstrated that polysilacage acid in single
crystals forms hydrogen-bonded dimers that consist of
the same enantiomers and forms layers similar to
smectic phase in liquid crystals. In addition, we have
found that esterification of the polysilacage is achievable
only under the Mitsunobu conditions with diisopropyl
azodicarboxylate. These findings open a new way for
exploration of novel liquid crystalline materials utilizing
polysilacage moiety as a core fragment.
[3] M. Shimizu, K. Watanabe, H. Nakagawa, T. Becker, S. Sugimoto,
T. Hiyama, Chem. Lett. (2001) 1090.
[4] D.L. Pavia, G.M. Lampman, G.S. Kriz, Introduction to Spectro-
scopy, Harcourt Brace College Publishers, Fort Worth, 1996, p. 62.
[5] Crystal data of 3: colorless plates: C18H45Si6O2, Mꢃ
monoclinic, space group C2/c, aꢃ9.5395(5), bꢃ16.2543(6), cꢃ
5549.5(6) A , Zꢃ8, Dcalc 1.106
2024.00, Tꢃ273 K, l(MoꢀKa)ꢃ0.71069 A,
0.062, Rwꢃ0.071, Goodness-of-fitꢃ1.95, p-
0.0400; Number of dataꢃ14 079, Number of unique
5705 (Rint 0.028).
/462.07,
/
/
/
3
˚
˚
35.884(3) A, bꢃ
(g cmꢁ3), F(0 0 0)ꢃ
2umax 54.28, Rꢃ
factorꢃ
dataꢃ
/
94.163(1)8, Vꢃ
/
/
ꢃ/
˚
/
/
/
/
ꢃ
/
/
/
/
/
/
/
ꢃ/
[6] B.M. Trost, G.S. Massiot, J. Am. Chem. Soc. 99 (1977)
4405.
5. Supplementary material
[7] T. Cohen, M. Bhupathy, Acc. Chem. Res. 22 (1989) 152.
[8] (a) O. Mitsunobu, Synthesis (1981) 1;
(b) D.L. Hughes, Org. React. 42 (1992) 335.
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic