Syntheses and Structural Characterizations of a Novel Bowl-Type Germanol and Its Derivatives

Article abstract of DOI:10.1246/bcsj.76.2389

A novel bowl-type triarylgermyl group, tris(2,2″,6,6″ -tetramethyl[1,1′:3′,1″-terphenyl]-5′-yl)germyl (denoted as TRMG), was designed, and a germanol and its derivatives bearing this framework were synthesized. X-ray crystallographic analysis of TRMG-OH (5) revealed that there is no OH...O hydrogen bonding between adjacent molecules, although the possible presence of a weak intermolecular OHmellip;π interaction was suggested. In sharp contrast to organogermanols known so far, 5 is extremely resistant to self-condensation; no digermoxane was obtained when 5 was subjected to the conditions under which Ph₃GeOH (8) affords the corresponding digermoxane. On the other hand, germanol 5 was readily converted to various derivatives. The crystal structure of TRMG-SH (12) was also determined.

Full text of DOI:10.1246/bcsj.76.2389

ꢀ 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 2389–2394 (2003) 2389
Syntheses and Structural Characterizations of a Novel Bowl-Type
Germanol and Its Derivatives
ꢀ
ꢀ
Kei Goto, Isao Shimo, and Takayuki Kawashima
Department of Chemistry, Graduate School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
Received May 30, 2003; E-mail: goto@chem.s.u-tokyo.ac.jp
A novel bowl-type triarylgermyl group, tris(2,200,6,600-tetramethyl[1,10:30,100-terphenyl]-50-yl)germyl (denoted as
TRMG), was designed, and a germanol and its derivatives bearing this framework were synthesized. X-ray crystallo-
graphic analysis of TRMG–OH (5) revealed that there is no OH O hydrogen bonding between adjacent molecules, al-
though the possible presence of a weak intermolecular OH ꢀ interaction was suggested. In sharp contrast to organoger-
ꢁꢁꢁ
ꢁꢁꢁ
manols known so far, 5 is extremely resistant to self-condensation; no digermoxane was obtained when 5 was subjected to
the conditions under which Ph3GeOH (8) affords the corresponding digermoxane. On the other hand, germanol 5 was
readily converted to various derivatives. The crystal structure of TRMG–SH (12) was also determined.
There have been a great number of reports on the structural
features of organosilanols as well as on the weak intermolecular
and intramolecular interactions found in their crystal
structures.1 In contrast, only limited information has been ac-
cumulated for the structures of analogous organogermanols,
presumably because their sensitivity toward self-condensation
is higher than that of organosilanols.2 In the course of our study
on the development and application of the bowl-shaped mole-
cules,3 we have designed a novel triarylmethyl group 1 (denot-
ed as Trm)4 and a triarylsilyl group 2 (denoted as TRMS)5,6
shown in Chart 1. In 1 and 2, the phenyl groups of a Ph3C
and Ph3Si group are replaced by the radially extended m-ter-
phenyl-50-yl groups, respectively, so that they would form a
shallow bowl-shaped cavity. The reactive species bearing the
Trm group can be prevented from dimerization or self-conden-
sation effectively, whereas its reactivity towards appropriate
molecules is not so much degenerated because there is a rela-
tively large space around it. A stable S-nitrosothiol (TrmSNO)
was successfully synthesized by taking advantage of the Trm
group.4 We also reported that silanol 4 bearing the TRMS
group is extremely resistant to self-condensation.5 Unlike the
[1,10:30,100-terphenyl]-50-yl)germyl; denoted as TRMG here-
after) will be useful as a novel germyl group possessing the
above-mentioned characteristics of the Trm and TRMS
groups. Here we report the syntheses, crystal structures, and re-
activities of germanol 5 and its derivatives bearing the TRMG
group.
Experimental
Melting points were determined on a Yanaco micro melting
point apparatus. All melting points are uncorrected. Et2O and
THF was purified by distillation from sodium diphenylketyl under
argon atmosphere before use. Benzene and decalin were distilled
from calcium hydride. Dioxane was purchased from Wako Pure
Chemical Industries Ltd. and used without purification. Prepara-
tive gel permeation liquid chromatography (GPLC) was performed
by LC-908 C60 and LC-918 with JAIGEL 1H and 2H columns
(Japan Analytical Industry) with chloroform as solvent. Column
chromatography was carried out with Wakogel C-200. 1H NMR
and 13C NMR spectra were recorded on a Bruker DRX-500 or a
JEOL JNM-A500 spectrometer. Infrared spectra were obtained
with a JASCO FT-IR420. For measurements of reflectance IR mi-
crospectra, an infrared microscope attachment, JASCO IRT-30,
was used. Elemental analyses were performed by the Microanalyt-
ical Laboratory of the Department of Chemistry, Faculty of Sci-
ence, the University of Tokyo. The preparations of 50-bromo-
2,200,6,600-tetramethyl-1,10:30,100-terphenyl (6)7 and Ph3GeOH (8)8
have been described in the literature.
usual organosilanols, 4 shows no OH O hydrogen bonding ei-
ther in the crystalline state or in solution. It is expected that
ꢁꢁꢁ
an analogous germyl group 3 (tris(2,200,6,600-tetramethyl-
Synthesis of Chlorotris(2,200,6,600-tetramethyl[1,10:30,100-ter-
phenyl]-50-yl)germane (TRMG–Cl, 7). To a solution of bromide
6 (1.00 g, 2.74 mmol) in Et2O (10 mL) was added dropwise n-BuLi
ꢃ
(1.69 M hexane solution, 1.7 mL, 2.87 mmol) at ꢂ78 C. After
ꢃ
stirring at ꢂ78 C for 30 min, the solution was warmed to room
temperature and again stirred for 30 min. The solution was cooled
to ꢂ78 ꢃC again, and then GeCl4 (95 mL, 0.833 mmol) was added
dropwise. The reaction mixture was stirred at ꢂ78 ꢃC for 1 h and
at room temperature overnight. After quenching by saturated
aqueous NH4Cl, the aqueous layer was extracted with CHCl3.
The combined organic layer was dried over anhydrous MgSO4,
Chart 1.
Published on the web December 15, 2003; DOI 10.1246/bcsj.76.2389

2390 Bull. Chem. Soc. Jpn., 76, No. 12 (2003)
Bowl-Type Germanol and Its Derivatives
ꢃ
1
and the solvent was removed under reduced pressure. The crude
product was purified by GPLC to give 7 (0.515 g, 0.534 mmol,
64%), which was further purified by recrystallization from
CHCl3–hexane.
7: colorless crystals, mp 269–270 ꢃC; 1H NMR (500 MHz,
CDCl3) ꢁ 1.94 (s, 36H), 7.04 (t, J ¼ 1:7 Hz, 3H), 7.05–7.14 (m,
18H), 7.42 (d, J ¼ 1:7 Hz, 6H); 13C NMR (126 MHz, CDCl3) ꢁ
20.81 (q), 127.21 (d), 127.29 (d), 131.92 (d), 132.81 (d), 134.99
(s), 135.73 (s), 140.98 (s), 141.54 (s). Found: C, 82.02; H,
6.70%. Calcd for C66H63ClGe: C, 82.21; H, 6.59%.
Synthesis of Tris(2,200,6,600-tetramethyl[1,10:30,100-terphen-
yl]-50-yl)germanol (TRMG–OH, 5). To a solution of 7 (0.380
g, 0.394 mmol) in THF (50 mL) was added NaOH (4.03 g, 0.101
mol) in H2O (50 mL) and the mixture was heated at reflux
temperature. After refluxing overnight, the reaction mixture was
extracted with CHCl3. The combined organic layer was dried over
anhydrous MgSO4, and the solvent was removed under reduced
pressure. The crude product was recrystallized from CHCl3–hex-
ane to give 5 (0.365 g, 0.385 mmol, 98%).
5: colorless crystals, mp 255–256 ꢃC; 1H NMR (500 MHz,
CDCl3) ꢁ 1.38 (s, 1H), 1.94 (s, 36H), 7.02 (t, J ¼ 1:6 Hz, 3H),
7.04–7.13 (m, 18H), 7.41 (d, J ¼ 1:6 Hz, 6H); 13C NMR (126
MHz, CDCl3) ꢁ 20.79 (q), 127.09 (d), 127.24 (d), 131.49 (d),
132.88 (d), 135.73 (s), 136.08 (s), 141.22 (s), 141.37 (s); IR ꢂOH
3609 cmꢂ1 (microcrystals from C6H6–hexane on the metal plate),
3609 cmꢂ1 (microcrystals from CHCl3–hexane on the metal plate),
3624 cmꢂ1 (5 mM and 20 mM CH2Cl2 solution). Found: C, 83.57;
H, 7.01%. Calcd for C66H64GeO: C, 83.81; H, 6.82%.
10: colorless crystals, mp 280–284 C (dec); H NMR (500
MHz, CDCl3) ꢁ 1.93 (s, 36H), 7.02 (t, J ¼ 1:6 Hz, 3H), 7.04–
7.14 (m, 18H), 7.41 (d, J ¼ 1:6 Hz, 6H); 13C NMR (126 MHz,
CDCl3) ꢁ 20.85 (q), 127.24 (d), 127.33 (d), 131.91 (d), 132.99
(d), 134.96 (s), 135.77 (s), 141.02 (s), 141.55 (s). Found: C,
78.32; H, 6.35%. Calcd for C66H63BrGe: C, 78.59; H, 6.30%.
Synthesis of Tris(2,200,6,600-tetramethyl[1,10:30,100-terphen-
yl]-50-yl)germane (TRMG–H, 11). To a solution of 7 (0.230
g, 0.238 mmol) ꢃin THF (5 mL) was added LiAlH4 (78.3 mg,
2.06 mmol) at 0 C, and the reaction mixture was stirred at room
temperature overnight. The resulting mixture was poured into
ice water and the aqueous layer was extracted with CHCl3. The
combined organic layer was dried over anhydrous MgSO4, and
the solvent was removed under reduced pressure to give 11
(0.223 g, 0.239 mmol, quant.), which was further purified by re-
crystallization from CHCl3–hexane.
11: white solids, mp 242–243 ꢃC; 1H NMR (500 MHz, CDCl3)
ꢁ 1.92 (s, 36H), 5.81 (s, 1H), 6.93 (t, J ¼ 1:6 Hz, 3H), 7.03–7.12
(m, 18H), 7.30 (d, J ¼ 1:6 Hz, 6H); 13C NMR (126 MHz, CDCl3)
ꢁ 20.77 (q), 126.98 (d), 127.19 (d), 130.46 (d), 133.86 (d), 135.63
(s), 135.77 (s), 141.14 (s), 141.48 (s). Found: C, 85.05; H, 7.07%.
Calcd for C66H64Ge: C, 85.25; H, 6.94%.
Synthesis of Tris(2,200,6,600-tetramethyl[1,10:30,100-terphen-
yl]-50-yl)germanethiol (TRMG–SH, 12).
A solution of 11
(0.613 g, 0.660 mmol) and S8 (23.5 mg, 0.0916 mmol) in decalin
(10 mL) was heated at reflux temperature for 5 d and then the sol-
vent was removed under reduced pressure. The crude product was
purified with GPLC to give 12 (0.451 g, 0.468 mmol, 71%), which
was further purified by recrystallization from CHCl3–hexane.
Comparison of the Reactivity of Germanols. To a solution of
Ph3GeOH (8) (0.100 g, 0.312 mmol) in C6H6 (30 mL) was added
anhydrous MgSO4 (1.00 g, 8.34 mmol) and the mixture was stirred
at reflux temperature for 12 h. The solvent was removed under re-
duced pressure and the crude product was purified with GPLC to
give Ph3GeOGePh3 (9) (0.0871 g, 0.140 mmol, 90%). The reac-
tion of TRMG–OH (5) (0.296 g, 0.313 mmol) under the same con-
ditions resulted in the quantitative recovery of 5. When a solution
of 5 (0.150 g, 0.159 mmol) in a mixed solvent of H2O (9 mL) and
dioxane (21 mL) was heated at 110 ꢃC for 12 h in the presence of
NaOH (0.43 g, 10.8 mmol), 5 was also recovered quantitatively.
Reaction of 5 with Acetyl Chloride. To the solution of 5
(0.234 g, 0.247 mmol) in C6H6 (10 mL) was added dropwise aceꢃtyl
ꢃ
1
12: colorless crystals, mp 263–265 C; H NMR (500 MHz,
CDCl3) ꢁ 0.21 (s, 1H), 1.92 (s, 36H), 6.99 (t, J ¼ 2 Hz, 3H),
7.04–7.13 (m, 18H), 7.37 (d, J ¼ 2 Hz, 6H); 13C NMR (126
MHz, CDCl3) ꢁ 20.79 (q), 127.12 (d), 127.27 (d), 131.26 (d),
133.00 (d), 135.76 (s), 136.60 (s), 141.22 (s), 141.37 (s). Found:
C, 82.27; H, 7.00; S, 3.47%. Calcd for C66H64GeS: C, 82.41; H,
6.71; S, 3.33%.
X-ray Crystallographic Analysis of 5a, 5b, and 12. Single
crystals of 5b and 12 were grown in their chloroform/hexane solu-
tion, while single crystals of 5a C6H14 were grown in their ben-
zene/hexane solution. The intensity data were collected at 120
K on a Rigaku/MSC Mercury CCD diffractometer with graphite-
ꢁ
ꢃ
ꢀ
chloride (1.00 mL, 17.7 mmol) at 50 C. After stirring at 50 C
monochromated Mo Kꢃ radiation (ꢄ ¼ 0:71069 A). Crystallo-
overnight, the solvent was removed under reduced pressure. The
crude product was recrystallized from CHCl3–hexane to give
chlorogermane 7 (0.230 g, 0.238 mmol, 96%).
graphic and experimental data are listed in Table 1. The structures
were solved by the direct method and refined by full-matrix least
squares on F2 using SHELXL 97.9 The non-hydrogen atoms were
refined anisotropically, except for the solvent molecule of
Reaction of 5 with Hydrochloric Acid. To a solution of 5
(0.200 g, 0.212 mmol) in C6H6 (20 mL) was added conc. hydro-
chloric acid (20 mL) and the mixture was heated at reflux
temperature. After refluxing overnight, the reaction mixture was
extracted with CHCl3 and the combined organic layer was dried
over anhydrous MgSO4. The solvent was removed under reduced
pressure, and the crude product was recrystallized from CHCl3–
hexane to give chlorogermane 7 (0.199 g, 0.207 mmol, 98%).
Synthesis of Bromotris(2,200,6,600-tetramethyl[1,10:30,100-ter-
phenyl]-50-yl)germane (TRMG–Br, 10). To a solution of 5
(0.208 g, 0.220 mmol) in C6H6 (20 mL) was added conc. hydrobro-
mic acid (20 mL) and the mixture was heated at reflux temperature.
After stirring overnight, the reaction mixture was extracted with
CHCl3. The combined organic layer was dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure.
The crude product was recrystallized from CHCl3–hexane to give
10 (0.204 g, 0.202 mmol, 92%).
5a C6H14 and the minor component of the two disordered 2,6-di-
ꢁ
methylphenyl rings of 5b (0.82:0.18 and 0.83:0.17, respectively).
The hydrogen atoms were idealized by using the riding models, ex-
cept for the OH hydrogens of 5b and the SH hydrogen of 12, which
were located in the difference Fourier map and then were refined
isotropically. Crystallographic data have been deposited at the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and copies
can be obtained on request, free of charge, by quoting the publica-
tion citation and the deposition numbers CCDC 218188–218190.
Results and Discussion
Chlorogermane 7 bearing the TRMG group was prepared by
the reaction of tetrachlorogermane with the aryllithium gener-
ated from m-terphenyl bromide 6 (Scheme 1). The alkaline hy-
drolysis of 7 in THF/water (1:1) at reflux temperature afforded

K. Goto et al.
Table 1. Crystallographic Data for 5a C6H14, 5b, and 12
Bull. Chem. Soc. Jpn., 76, No. 12 (2003) 2391
ꢁ
5a C6H14
ꢁ
5b
12
Formula
C72H78GeO
120
C66H64GeO
120
C66H64GeS
120
Temperature/K
Crystal system
Space group
monoclinic
C2=c
monoclinic
P21=n
monoclinic
P21=c
ꢀ
a/A
31.102(13)
15.436(6)
26.603(12)
110.038(6)
11999(9)
8
1.143
37516
10336
0.0387
4400
18.220(5)
24.388(6)
24.241(6)
97.893(4)
10669(5)
8
1.178
67998
18431
0.0311
4000
12.172(4)
24.854(7)
17.898(5)
97.778(3)
5365(3)
4
1.191
34140
9351
ꢀ
b/A
ꢀ
c/A
ꢅ/deg
ꢀ 3
V/A
Z
Calculated density/g cmꢂ3
Reflections collected
Unique
Rint
F000
0.0299
2032
Limiting indices
ꢂ29 ꢄ h ꢄ 36
ꢂ15 ꢄ k ꢄ 18
ꢂ31 ꢄ l ꢄ 31
0/661
ꢂ21 ꢄ h ꢄ 20
ꢂ29 ꢄ k ꢄ 29
ꢂ26 ꢄ l ꢄ 28
0/1322
ꢂ12 ꢄ h ꢄ 14
ꢂ29 ꢄ k ꢄ 26
ꢂ21 ꢄ l ꢄ 21
0/632
Restraints/parameters
Goodness of fit (F2)
R indices (I > 2ꢆðIÞ)
1.081
1.187
1.103
R1 ¼ 0:0603
wR2 ¼ 0:1473
R1 ¼ 0:0673
wR2 ¼ 0:1522
R1 ¼ 0:0457
wR2 ¼ 0:1131
R1 ¼ 0:0552
wR2 ¼ 0:1179
R1 ¼ 0:0474
wR2 ¼ 0:1054
R1 ¼ 0:0527
wR2 ¼ 0:1082
R indices (all data)
Scheme 1.
germanol 5 almost quantitatively. The IR spectrum of 5
(CH2Cl2) shows an absorption at 3624 cmꢂ1, which is assign-
able to a free OH. This band was found to be concentration-in-
dependent, indicating that germanol 5 has a monomeric struc-
1
ture in solution. In the H NMR spectrum of 5, the OH reso-
nance was observed at ꢁ ¼ 1:38. The equivalency of all the
methyl protons of the 2,6-dimethylphenyl groups at room tem-
perature shows that the Ge–C bonds rotate rapidly on the NMR
time-scale.
Fig. 1. ORTEP drawing of germanol 5a (50% probability).
The sovlent molecule is omitted for clarity.
TRMS–OH (4)5 obtained from the same solvent system (ben-
zene–hexane); it belongs to the monoclinic space group C2=c
with Z ¼ 8 and one molecule of hexane is included in the
asymmetric unit. The most important feature to be noticed is
The structure of 5 was established by X-ray crystallographic
analysis. In large cavity-shaped compounds, the growth of sin-
gle crystals often depends on the solvent utilized for re-
crystallization. Two different types of single crystals of 5 were
obtained from different solvents, 5a (from a mixture of benzene
and hexane) and 5b (from a mixture of chloroform and hexane).
The crystal structures of 5a and 5b are shown in Figs. 1 and 2,
respectively. The selected bond lengths and angles for 5a and
5b are given in Table 2. In both structures, the OH group is
located in the center of a shallow bowl-shaped cavity formed
by three m-terphenyl units.
the absence of any OH O hydrogen bonding. It is well-recog-
nized that germanols have a strong tendency to form intermo-
ꢁꢁꢁ
lecular OH O hydrogen bonding to give oligomeric structures
ꢁꢁꢁ
in the crystalline state.2 For example, Ph3GeOH (8) was report-
ed to have a tetrameric structure with the intermolecular O O
ꢀ
ꢁꢁꢁ
2b
distances between 2.60 and 2.66 A. In sharp contrast, the
ꢀ
shortest O O distance of 5a is 7.77 A. There have been a
ꢁꢁꢁ
few examples of the germanols which have no intermolecular
ꢁꢁꢁ
The crystal structure of 5a is isomorphous with that of
OH O hydrogen bridge in the crystalline state.2c,10 In these

2392 Bull. Chem. Soc. Jpn., 76, No. 12 (2003)
Bowl-Type Germanol and Its Derivatives
cases, however, intramolecular hydrogen bonding to hetero-
ꢁꢁꢁ
atoms such as nitrogen2c or intramolecular OH ꢀ interaction
between the GeOH group and an aromatic ring in the same
molecule10 was observed. For several sterically hindered sila-
nols including TRMS–OH (4),5 an intermolecular OH ꢀ inter-
ꢁꢁꢁ
action between the SiOH group and the aromatic ring of the ad-
jacent molecule was observed.11 Examination of the crystal
structure of germanol 5a suggested the possible presence of
the same type of intermolecular OH ꢀ interaction as that ob-
ꢁꢁꢁ
served for silanol 4. Although the OH hydrogen atom of 5a
could not be unequivocally located, the oxygen atom lies above
the C(30)–C(31) bond of the aromatic ring in the adjacent
molecule. This arrangement is almost the same as that ob-
served in the crystal structure of silanol 4. The distances of
ꢀ
O(1) C(31) and O C(30) are 3.29 and 3.34 A, respectively,
ꢁꢁꢁ ꢁꢁꢁ
which are similar to the corresponding atomic distances in sila-
ꢀ
nol 4 (3.27 and 3.37 A).
5
The crystal structure of 5b shows that it belongs to the mon-
oclinic space group P21=n with Z ¼ 8. There are two inde-
pendent molecules of TRMG–OH in the asymmetric unit,
whereas no solvent molecule is included. For 5b, the OH hy-
drogen atoms were located in the difference Fourier map and
refined isotropically. The shortest O O distance of 5b is
ꢀ
9.21 A, indicating that there is no OH O hydrogen bonding al-
ꢁꢁꢁ
ꢁꢁꢁ
so for 5b. As for the intermolecular OH ꢀ interaction, the sit-
ꢁꢁꢁ
uation for 5b is more delicate. In both fragments of 5b, the O–
H bond is directed towards the region above one of the C–C
bonds of the aromatic ring in the adjacent molecule (Fig. 3).
However, the OH C distances are 2.86 (H(1) C(83)), 2.80
ꢁꢁꢁ
ꢁꢁꢁ
ꢀ
(H(1) C(84)), 2.91 (H(2) C(17)), and 3.06 A (H(2) C(18)),
ꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁ
which seem somewhat long for OH ꢀ interaction.11 Concom-
itantly, the corresponding O C distances of between 3.45 and
ꢀ
3.77 A are longer than those of 5a. The IR microspectroscopy
ꢁꢁꢁ
measurements for the microcrystals of both 5a and 5b showed
the OH band at 3609 cmꢂ1, which is only 15 cmꢂ1 lower than
that in solution. These results indicate that the presence of the
Fig. 2. (a) ORTEP drawing of germanol 5b (50%
probability). The disordered aromatic rings are omitted
for clarity. (b) Space filling model of the crystal structure
of 5b (one of two independent molecules).
intermolecular OH ꢀ interactions in the crystals of 5a and 5b
ꢁꢁꢁ
cannot be ruled out, but they are very weak if they are present at
all.
The crystal structures of 5a and 5b suggest that the bowl-
shaped framework of the TRMG group sterically prevents the
ꢀ
Table 2. Selected Bond Lengths (A) and Angles (deg) for 5a and 5b
5a
5b
Bond lengths
O(1)–H(1)
0.70(3)
O(2)–H(2)
0.77(3)
Ge(1)–O(1)
Ge(1)–C(1)
Ge(1)–C(23)
Ge(1)–C(45)
1.786(2)
1.939(3)
1.931(3)
1.946(3)
Ge(1)–O(1)
Ge(1)–C(1)
Ge(1)–C(23)
Ge(1)–C(45)
1.7852(18)
1.935(2)
1.943(2)
1.951(2)
Ge(2)–O(2)
Ge(2)–C(75)
Ge(2)–C(97)
Ge(2)–C(127)
1.7853(17)
1.938(2)
1.945(2)
1.949(2)
Bond angles
Ge(1)–O(1)–H(1)
O(1)–Ge(1)–C(1)
O(1)–Ge(1)–C(23)
O(1)–Ge(1)–C(45)
C(1)–Ge(1)–C(23)
C(23)–Ge(1)–C(45)
C(45)–Ge(1)–C(1)
114(3)
Ge(2)–O(2)–H(2)
113(2)
O(1)–Ge(1)–C(1)
O(1)–Ge(1)–C(23)
O(1)–Ge(1)–C(45)
C(1)–Ge(1)–C(23)
C(23)–Ge(1)–C(45)
C(45)–Ge(1)–C(1)
111.61(11)
105.96(11)
110.67(12)
112.76(13)
109.43(12)
106.46(12)
105.68(9)
109.58(9)
108.83(9)
112.63(9)
108.52(9)
111.51(9)
O(2)–Ge(2)–C(75)
O(2)–Ge(2)–C(97)
O(2)–Ge(2)–C(127)
C(75)–Ge(2)–C(97)
C(97)–Ge(2)–C(127)
C(127)–Ge(2)–C(75)
104.54(9)
108.91(9)
108.54(8)
113.94(9)
108.20(8)
112.51(9)

K. Goto et al.
Bull. Chem. Soc. Jpn., 76, No. 12 (2003) 2393
Scheme 2.
Scheme 3.
Chlorogermane 7 was also obtained by the reaction of 5 with
acetyl chloride. Reduction of 7 with LiAlH4 afforded hydro-
germane 11, which was further converted to germanethiol 12
in a good yield by heating with elemental sulfur in decalin.
These results demonstrate that the bowl-shaped framework of
the TRMG group prevents the self-condensation reaction effec-
tively without diminution of the reactivity of the central func-
tional group towards appropriate reagents.
The molecular structure of germanethiol 12 was determined
by X-ray crystallography to be as shown in Fig. 4. Selected
bond lengths and angles are listed in Table 3. Structural ana-
lyses of a triorganogermanethiol are few: only the crystal struc-
ture of tricyclohexylgermanethiol (13)13 has been reported so
Fig. 3. Diagram of an array of germanol 5b in the crystals.
formation of the OH O hydrogen bonding. Unlike usual bulky
ꢁꢁꢁ
substituents, however, the TRMG group does not increase the
steric congestion around the GeOH center of 5a and 5b so much
in comparison with Ph3GeOH (8) because there is no ortho-
substituent on the aromatic rings connected to the germanium
atom in 5. The mean values of C–Ge–C bond angles are
109.6ꢃ for 5a and 110.9ꢃ and 111.6ꢃ for two fragments of 5b,
respectively, which are similar to that of 8 (111.6ꢃ, a mean val-
ue of eight fragments)2b and much smaller than that of
Mes3GeOH in Mes3GeOH Mes3GeNCO (Mes = 2,4,6-tri-
ꢁ
methylphenyl) adduct (114.7ꢃ).12 In germanol 5 bearing a den-
dritic framework, the molecular size is enlarged in comparison
to 8 without increasing steric repulsions among the three aryl
groups.
Usually, organogermanols show high sensitivity towards
self-condensation. Actually, when a benzene solution of
Ph3GeOH (8) was stirred in the presence of anhydrous MgSO4
for 12 h at reflux temperature, 8 was converted to digermoxane
9 almost quantitatively (Scheme 2). In sharp contrast to 8, no
condensation product was obtained when TRMG–OH (5) was
ꢃ
treated under the same conditions. Upon heating at 110 C
in the presence of NaOH in water/dioxane, 5 also underwent
no self-condensation. In spite of such high stability towards
condensation, 5 can readily be converted to various derivatives.
Treatment of 5 with hydrochloric or hydrobromic acid in ben-
zene afforded the corresponding chlorogermane 7 or bromoger-
mane 10, respectively, in almost quantitative yields (Scheme 3).
Fig. 4. ORTEP drawing of germanethiol 12 (50% probability).

2394 Bull. Chem. Soc. Jpn., 76, No. 12 (2003)
Bowl-Type Germanol and Its Derivatives
ꢀ
Table 3. Selected Bond Lengths (A) and Angles (deg) for 12
References
1
2
P. D. Lickiss, Adv. Inorg. Chem., 42, 147 (1995).
a) H. Puff, S. Franken, W. Schuh, and W. Schwab, J. Orga-
Bond lengths
Bond angles
Ge(1)–S(1)–H(1)
S(1)–H(1)
1.13(4)
95(2)
nomet. Chem., 254, 33 (1983). b) G. Ferguson, J. F. Gallagher, D.
Murphy, T. R. Spalding, C. Glidewell, and H. D. Holden, Acta
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and K. Tamao, Organometallics, 16, 5102 (1997). d) J. Beckmann,
K. Jurkschat, and M. Shurmann, Eur. J. Inorg. Chem., 2000, 939.
e) Y. Zhang, F. Cervantes-Lee, and K. H. Pannell, Organometal-
lics, 22, 510 (2003).
Ge(1)–S(1)
Ge(1)–C(1)
Ge(1)–C(23)
Ge(1)–C(45)
2.2284(9)
1.951(2)
1.939(2)
1.944(2)
S(1)–Ge(1)–C(1)
S(1)–Ge(1)–C(23)
S(1)–Ge(1)–C(45)
C(1)–Ge(1)–C(23)
C(23)–Ge(1)–C(45)
C(45)–Ge(1)–C(1)
109.14(7)
103.79(8)
110.19(8)
112.93(10)
112.10(10)
108.59(9)
¨
3
For examples, see: a) K. Goto, N. Tokitoh, and R. Okazaki,
Angew. Chem., Int. Ed. Engl., 34, 1124 (1995). b) K. Goto, M.
Holler, and R. Okazaki, J. Am. Chem. Soc., 119, 1460 (1997). c)
T. Saiki, K. Goto, and R. Okazaki, Angew. Chem., Int. Ed. Engl.,
36, 2223 (1997). d) K. Goto and R. Okazaki, Liebigs Ann./Recl.,
1997, 2393 (Microreview). e) K. Goto, Y. Hino, Y. Takahashi,
T. Kawashima, G. Yamamoto, N. Takagi, and S. Nagase, Chem.
Lett., 2001, 1204.
4 K. Goto, Y. Hino, T. Kawashima, M. Kaminaga, E. Yano,
G. Yamamoto, N. Takagi, and S. Nagase, Tetrahedron Lett., 41,
8479 (2000).
far, and that of 12 is the first example for a triarylgermanethiol.
ꢀ
The Ge–S bond length of 2.2284(9) A in 12 is very close to that
13
in 13 (2.253(2) A). The mean value of the C–Ge–C bond an-
ꢀ
gles in 12 is 111.2ꢃ, which is similar to that of germanol 5.
Conclusion
A novel bowl-type germyl group 3, a TRMG group, was de-
signed as the germanium analogue of the Trm and TRMS
groups, and a germanol and its derivatives bearing this frame-
work were synthesized. In the crystal structure of germanol 5,
5 K. Goto, T. Okumura, and T. Kawashima, Chem. Lett.,
2001, 1258.
6
Recently, Maruoka et al. reported a tris(2,6-diphenylben-
no OH O hydrogen bonding was observed, although the possi-
ble presence of a weak intermolecular OH ꢀ interaction was
ꢁꢁꢁ
zyl)silyl group as a highly crowded bowl-shaped protective group:
A. Iwasaki, Y. Kondo, and K. Maruoka, J. Am. Chem. Soc., 122,
10238 (2000).
ꢁꢁꢁ
suggested. In sharp contrast to organogermanols known so
far, 5 is extremely resistant to self-condensation; no digermox-
ane was obtained when 5 was subjected to the conditions under
which Ph3GeOH (8) affords the corresponding digermoxane.
On the other hand, germanol 5 as well as its derivatives readily
reacted with appropriate reagents. Further investigations are
underway on the application of the TRMG group to the steric
protection of reactive species as well as on the syntheses of
the metal complexes using germanol 5 and germanethiol 12
as novel-type of bulky ligands.
7
a) C.-J. F. Du, H. Hart, and K.-K. D. Ng, J. Org. Chem., 51,
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8
9
ture refinement,’’ University of Gottingen (1997).
¨
10 a) B. E. Eichler, D. R. Powell, and R. West, Organometal-
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`
12 G. Hihara, R. C. Hynes, A.-M. Lebuis, M. Riviere-Baudet,
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This work was partly supported by Grants-in-Aid for The
21st Century COE Program for Frontiers in Fundamental
Chemistry (T.K.) and for Scientific Research (Nos. 14703066
(K.G.) and 15105001 (T.K.)) from the Ministry of Education,
Culture, Sports, Science and Technology. We also thank Tosoh
Finechem Corporation for the generous gifts of alkyllithiums.
(2000).
´
´
13 F. Brisse, F. Belanger-Gariepy, B. Zacharie, Y. Gareau, and
K. Steliou, Nouv. J. Chim., 7, 391 (1983).