Stepwise synthesis and characterization of germa[4], [5], [8], and [10]pericyclynes

Article abstract of DOI:10.1039/c5dt01411e

The stepwise syntheses of germa[N]pericyclynes, including [5]pericyclynes, and their characterization are described. The yields of germa[4] and [8]pericyclynes were improved significantly compared to those obtained in previous studies. The routes reported

Full text of DOI:10.1039/c5dt01411e

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Stepwise synthesis and characterization of
germa[4], [5], [8], and [10]pericyclynes†
Cite this: Dalton Trans., 2015, 44,
11811
Hiroki Tanimoto,* Tomohiko Nagao, Taro Fujiwara, Yasuhiro Nishiyama,
Tsumoru Morimoto, Toshimasa Suzuka,‡ Ken Tsutsumi§ and Kiyomi Kakiuchi*
The stepwise syntheses of germa[N]pericyclynes, including [5]pericyclynes, and their characterization are
described. The yields of germa[4] and [8]pericyclynes were improved significantly compared to those
obtained in previous studies. The routes reported herein afforded the novel germa[5] and [10]pericyclynes,
which were characterized by X-ray crystallography, UV-Vis spectroscopy, and fluorescence emission
spectroscopy. A unique fluorescence emission was observed for the large germa[10]pericyclyne ring.
Received 14th April 2015,
Accepted 8th May 2015
DOI: 10.1039/c5dt01411e
www.rsc.org/dalton
Introduction
The acetylene unit, especially as polyynes, has long been
focused in materials science, and as building blocks of
peculiar structural molecules in synthetic, and physical
organic chemistry.1,2 In recent decades, cyclic skipped polyyne
compounds called [N]pericyclynes,3–7 which are composed of
N-acetylenic units, have received a growing amount of atten-
tion. As the reduced bond angles of the vertex sp3 atoms in
pericyclynes are considered to reinforce the through-space
interaction between skipped alkynes, such characteristics
result in unique electronic and optical properties. To develop
pericyclyne chemistry facilitating the hyperconjugation of
alkynes8 and the heavy atom effect of vertexes, we previously
reported the synthesis and characterization of germa[N]peri-
cyclynes, novel pericyclynes containing the group 14 element
germanium (Fig. 1).9 It was demonstrated that such compounds
were efficient building blocks for incorporation into functional
materials and polymers. However, our previous one-step syn-
thesis unselectively afforded [4], [6], and [8]pericyclynes in low
yields. Moreover, this method was not suitable for the prepa-
ration of [5]pericyclynes, containing an odd number of germa-
nium atoms. Since the small [4] and [5]pericyclynes are
Fig. 1 Germa[N]pericyclynes.
expected to show specific properties due to their reduced vertex
angles, their syntheses and characterization are of particular
interest. In contrast, germa[8]pericyclynes were revealed to
display unique fluorescence emission patterns in fluorescence
spectra and we believe that such interesting behaviour was
worth investigation through the synthesis of large ring germa-
pericyclynes. We herein report the improved stepwise synthesis
of germa[N]pericyclynes, including germa[4], [5], [8], and
[10]pericyclynes, and their characterization by X-ray crystallo-
graphy, UV-Vis spectroscopy, and fluorescence spectroscopy.
Results and discussion
We first performed the stepwise synthesis of germaperi-
cyclynes from diethynylgermanes 1a–b.9 To monoanions of
1a–b, generated by the addition of n-butyllithium, was added
0.5 eq. of the appropriate germanium dichloride to give tri-
meric compounds 2a–b (Scheme 1). Monoacetylidation of 2a–b
Graduate School of Materials Science, Nara Institute of Science and Technology
(NAIST), 8916-5 Takayamacho, Ikoma, Nara 630-0192, Japan.
E-mail: tanimoto@ms.naist.jp, kakiuchi@ms.naist.jp; Fax: +81 743 72 6089;
Tel: +81 743 72 6084
†Electronic supplementary information (ESI) available: NMR, UV-visible, fluo-
rescence emission spectra, CV (DPV), and crystallographic data. CCDC with ethyl magnesium bromide followed by coupling with 1
1057090–1057093. For ESI and crystallographic data in CIF or other electronic
eq. of the germanium dichloride and subsequent ethynylation
afforded tetragermanes 3a–b. With precursors 2 and 3 in
hand, we conducted the macrocyclization reaction to give the
format see DOI: 10.1039/c5dt01411e
‡Present address: Department of Chemistry, University of the Ryukyus,
Nishihara, Okinawa 903-0213, Japan.
germapericyclynes. Slow addition of diphenylgermanium
§Present address: Department of Chemistry, Tokyo Metropolitan University,
1-1 Minami-osawa, Hachioji, Tokyo 192-0397, Japan.
dichloride to dilithiated 2a via a syringe pump afforded 4a and
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conformations, while [4]pericyclyne 4a was previously found to
be planar.9 The smallest C–Ge–C angles of 6a–b were compar-
able to 4a (4a: 103.66(10)°,9 6a: 104.1(3)°, 6b: 103.58(18)°),
while the largest C–Ge–C angles were 107.6(3)° for 6a and
109.01(19)° for 6b, respectively. The Ge–CuC angles were
found to vary between 170.2(8)° and 178.6(6)° (6a), and
between 166.0(4)° and 176.8(4)° (6b). From these results, it
Scheme 1 Synthesis of germa[4], [5], [8] and [10]pericyclynes via step-
wise route.
5a in 12% and 23% yields, respectively. Addition over 5 min
via a dropping funnel gave 4a and 5a in only 4% and 17%
yields, respectively. The overall yields of both 4a (10%) and 5a
(18%) from 1a via the stepwise route were significantly
improved in comparison with the previous one-step syntheses
(3% and 10% for 4a and 5a, respectively). In addition, the [8]
pericyclyne 5b was isolated from 2b in 15% overall yield via
the stepwise route, compared to 13% yield in a single step syn-
thesis. The isolation of [4]pericyclyne 4b was not successful via
the stepwise approach. For the successful preparation of the
germa[5]pericyclynes 6a–b and [10]pericyclynes 7a–b from 3a–b,
high-dilution reaction conditions were required. Considering
the unsuccessful result to synthesize 4b, the low yield of 6b
could be attributed to the presence of the bulky isopropyl
groups suppressing the formation of the cyclic species. For
comparison, reference compounds 8a–b were also prepared by
masking 1a–b with the trimethylgermyl group.
Following their first successful synthesis, X-ray crystallo-
graphy of the germa[5] 6a–b and [10]pericyclynes 7a–b was
carried out (Fig. 2). [5]Pericyclynes 6a–b displayed envelope
Fig. 2 ORTEP drawing of germa[5] and [10]pericyclynes; (a) 6a; (b) 7a;
(c) 6b; (d) 7b.
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could be concluded that 6a–b exhibited greater strain than
methylated sila[5]pericyclynes (average C–X–C and X–CuC
angles: 106.0° and 175.1° (6a), 106.2° and 172.2° (6b), cf.
106.1° and 177.2° (Me-sila[5])4f), and were not bent to the
extent of 4a (103.8° and 172.3°). In contrast, [10]pericyclynes
7a–b were present in zigzag forms,9 with 7a displaying intra-
molecular π–π interactions between the phenyl rings present
in its cavity. From X-ray data, the estimated distance between
phenyl rings in the cavity of 7a was approximately 3.5–3.8 Å
with full ring overlap while that of 5a9 was 3.5 Å with only
partial overlap.
UV-Vis and fluorescence emission spectra of [5]pericyclynes
6a–b and [10]pericyclynes 7a–b were recorded in dichloro-
methane and hexane, and were compared to a range of other
germapericyclynes.9 Both 6a and 7a showed comparable
absorption maxima (261 nm, ε = 2540 (6a), 5070 (7a)) to the
other phenyl germapericyclynes9 (Fig. 3a, see the ESI† for
details). In addition, it was observed that the ε values
increased with an increase in the number of benzene rings.
Although it is expected that 6a and 7a also have absorption
bands at short wavelengths, measurement was problematic
due to solubility issues. In the UV-Vis spectra of hexane-
soluble 6b and 7b (Fig. 3b), shoulders were observed at
205 nm (ε = 14 500 (6b), 28 900 (7b)) and 213 nm (ε = 10 600
(6b), 23 200 (7b)), as reported for [6]pericyclyne 9b and [8]peri-
cyclyne 5b9 (for detailed values, see the ESI†). When compared
to compound 8b (203 nm: ε = 4330, 210 nm: ε = 2994) and 1b,9
where no such peaks were present, these shoulders could be
assigned to the internal germanium-substituted alkynes, as
observed for the silapericyclynes.4g It appeared that the ring
size did not affect the spectra;10 however, a small bathochro-
mic shift between compounds 8b and 7b (Fig. 3b) suggested
the influence of cyclic structures or ring strain.4f
Strain within the alkyne structure could also be estimated
by Raman spectroscopy.11 According to the reported trends,
[4]pericyclyne 4a was found to contain the most-strained alkynes
(4a: 2107 cm−1) followed by [5]pericyclyne (6a: 2110 cm−1
)
Fig. 3 UV-visible spectra, (a) 0.1 mM in CH2Cl2, (b) 0.1 mM in hexane;
and fluorescence emission spectra, (c) 0.1 mM in CH2Cl2. λex = 260 nm
(solid lines), λex = 273.5 nm (dashed lines), (d) normalized differential
among the phenyl compounds, while the values for [6], [8],
and [10]pericyclynes were comparable (9a: 2114, 5a: 2112,9 7a:
2113 cm−1). However, isopropyl compounds gave opposite
results, with the band for [5]pericyclyne (6b: 2103 cm−1) found
at a higher wavenumber than comparable [6], [8], and [10]peri-
cyclynes (9b: 2099, 5b: 2098, 7b: 2098 cm−1). The reason is not
clear so far because of few referential examples.
The fluorescence emission maxima of the germa[5]peri-
cyclyne 6a were found to be similar to the [4] and [6]peri-
cyclynes (4a and 9a) (λ = 282, 288 nm) (Fig. 3c).9 However,
unlike [4], [5], and [6]pericyclynes (4a, 6a, and 9a), [10]peri-
cyclynes 7a also displayed emission at 318 nm as well as
[8]pericyclynes 5a. This difference was displayed clearly in the
normalized differential spectra (Fig. 3d). Changing the exci-
tation wavelength from 260 to 273.5 nm increased the emis-
sion intensities of 5a and 7a at approximately 320 nm, whereas
no significant changes were observed for 4a, 6a, or 9a. Because
the characteristic emissions could be assigned to absorption
around 265 nm (Fig. 3e), the emissions were likely derived from
spectra based on 1a, λex = 260 nm, (e) excitation spectra, 5a: λex
321.5 nm, 7a: λex = 320 nm.
=
the excimer, by intramolecular π–π stacking of the benzene
rings, as indicated in Fig. 2b. It is expected that the larger ring
size of 7a compared to 5a allows stronger π–π interactions. Fluo-
rescence emission quantum yields were not recorded because
the emissions were observed at only short wavelengths.
From cyclic voltammetry and differential pulse voltammetry
DPV
OX
(DPV) (Fig. 4), oxidation potentials (E
= 1.38 V (6a, Ph-[5]),
1.36 V (7a, Ph-[10]), 1.27 V (6b, iPr-[5]), and 1.26 V (7b, iPr-[10]))
were found to be comparable to those previously reported for
the germa[4], [6], and [8]pericyclynes.9 In addition, the oxi-
dation potentials of isopropyl compounds 6b and 7b were
found to be smaller than those of the corresponding phenyl
compounds 6a and 7a.
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and the phenyl groups through the germanium atoms are also
shown for 6a. As was the case for the [6]pericyclynes,9 out-of-
plane HOMOs are found in 6b, while the [4]pericyclynes9
display in-plane orbitals. In contrast, the orbitals of 6a are
located close to the benzene rings.
Conclusions
Germa[4], [5], [8], and [10]pericyclynes were synthesized via a
stepwise route, giving an improvement in yield over our pre-
viously reported one-step synthetic route. Novel germa[5] and
[10]pericyclynes were characterized by X-ray crystallography,
cyclic voltammetry, UV-Vis spectroscopy, and fluorescence
emission spectroscopy. The unique fluorescence behaviour of
phenylgerma[10]pericyclyne is reported, and the frontier orbi-
tals of [5]pericyclynes were estimated by DFT calculations. Our
improved synthesis and optical investigation of cyclic skipped
oligo-alkyne compounds may open the door to further studies
into the chemistry and design of functional organic–inorganic
hybrid materials.
Experimental
General procedures
1H and 13C NMR spectra were recorded using a JEOL
JNM-ECP500 spectrometer (500 MHz for 1H NMR and
126 MHz for 13C NMR). Chemical shifts are reported as
δ values in ppm and calibrated with respect to the residual
solvent peak (CDCl3, δ 7.26 for 1H NMR and δ 77.00 for
Fig. 4 Cyclic and differential pulse voltammograms of germa[5] and
[10]pericyclynes 6a–b and 7a–b (1.0 mM in 0.1 M n-Bu4NPF6−CH2Cl2
solution; scan rate = 0.1 V s−1).
DFT calculations for germa[5]pericyclynes 6a–b (Fig. 5)
show the through-space interactions between alkynes in the
LUMO of 6b. Delocalized orbitals between the alkyne moieties
1
13C NMR) or tetramethylsilane (δ 0 for H NMR). The abbrevi-
ations used are as follows: s (singlet), d (doublet), t (triplet),
q (quartet), sept (septet), br (broad peak), and m (complex
multiplet). Melting points were measured using a Yanaco
Micro melting point apparatus. Infrared spectra were
measured using a JASCO FT-IR-4200 spectrometer. Mass
spectra were recorded using
a JEOL JMS-700 MStation
[EI (70 eV), CI, FAB, and ESI]. X-ray crystal analyses were per-
formed using a Rigaku R-AXIS RAPID/S imaging plate diffracto-
meter. Raman spectra were obtained using a JASCO laser
Raman spectrophotometer, NRS-2100. The cyclic voltammetry
measurements of the compounds were performed using a BAS
electrochemical analyser ALS612D in dichloromethane con-
taining n-Bu4NPF6 as the supporting electrolyte at 298 K
(100 mV s−1). The glassy carbon working electrode was
polished using the BAS polishing alumina suspension and
rinsed with water before use. The counter electrode was a plati-
num wire. The measured potentials were recorded with respect
to Ag/AgNO3 and normalized with respect to Fc/Fc+. Flash
column chromatography was performed using Merck Silica gel
60. The progress of the reactions was monitored by silica gel
thin layer chromatography (TLC) (Merck TLC Silica gel 60 F254
)
with an iodine/silica gel stain. The purification of the mixture
of germapericyclynes was performed using a LC-908 recycling
preparative high-performance liquid chromatography (HPLC)
Fig. 5 Molecular orbitals for the germa[5]pericyclynes 6a and 6b
obtained by DFT calculations (Gaussian 09 B3LYP/6-31G(d,p)).
11814 | Dalton Trans., 2015, 44, 11811–11818
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equipped with a JAIGEL 2H-40 column (chloroform elution) under a nitrogen atmosphere. The reaction mixture was stirred
made by Japan Analytical Industry Co., Ltd. Anhydrous tetra- for 1 h at the same temperature, and then the reaction mixture
hydrofuran (THF) was purchased from Kanto Chemical, which was warmed up to ambient temperature and stirred for 2 h.
was further dehydrated over activated molecular sieves 4A. The reaction mixture was cooled down to −78 °C and dichloro-
Density functional theory (DFT) calculations were performed diphenylgermane (414 mg, 1.39 mmol) was added. The reac-
using the Gaussian09, and the geometries of the molecules tion mixture was warmed up to ambient temperature and
were optimized by employing the B3LYP density functionals stirred for 17 h. The reaction mixture was cooled down to 0 °C
and the 6-31G(d,p) basis set in this series of calculations.
and ethynylmagnesium bromide (0.5 M in THF, 3.48 mL,
Bis((ethynyldiphenylgermyl)ethynyl)diphenylgermane (2a). 1.74 mmol) was added. After that, the reaction mixture was
n-Butyllithium (1.63 M in hexane, 3.21 mL, 5.24 mmol) was warmed up to ambient temperature and stirred for 9 h. The
added dropwise to a stirred solution of diethynyldiphenyl- reaction was quenched with a saturated aqueous solution of
germane 1a9 (1.45 g, 5.24 mmol) in THF (52 mL) at −78 °C under ammonium chloride at 0 °C. The mixture was extracted with
a nitrogen atmosphere. After 2 h, dichlorodiphenylgermane dichloromethane and washed with brine. The combined
(744 mg, 2.50 mmol) was added at the same temperature. organic layer was dried over magnesium sulfate, and the
Then the reaction mixture was warmed up to ambient temp- solvent was removed in vacuo. The residue was purified by
erature and stirred for 13 h. The reaction was quenched with a silica gel column chromatography (hexane/dichloromethane =
saturated aqueous solution of ammonium chloride at 0 °C. 4/1 to 3/1) to afford 3a (233 mg, 16%). White solid; Rf value
The mixture was extracted with ether, and the organic layer 0.26 (hexane/dichloromethane = 2/1); m.p. 132.6–134.9 °C;
was washed with water and brine. The combined organic layer IR (KBr, disc) νmax 3275, 3069, 3045, 2035, 1484, 1432,
1
was dried over magnesium sulfate, and the solvent was 1095 cm−1; H NMR (500 MHz, CDCl3) δ 7.73–7.69 (m, 16H),
removed in vacuo. The resulting residue was purified by silica 7.43–7.35 (m, 24H), 2.586 (s, 2H); 13C NMR (126 MHz, CDCl3)
gel column chromatography (hexane/dichloromethane = 10/1 δ 133.8, 133.7, 133.4, 133.1, 130.1, 130.0, 128.6, 128.5, 107.9,
to 3/1) to afford 2a (1.57 g, 80%). White solid; Rf value 107.7, 107.4, 95.2, 82.6; LRMS (ESI, M = C58H42Ge4) m/z = 1053
0.3 (hexane/dichloromethane = 3/1); m.p. 123.7–124.6 °C; [M + Na]+. Anal. Calcd for C58H42Ge4: C, 67.67; H, 4.11. Found:
IR (KBr, disc) νmax 3273, 3070, 3028, 2035, 1485, 1433, 1095, C, 67.58; H, 4.18.
736 cm−1
;
1H NMR (500 MHz, CDCl3) δ 7.73–7.70 (m, 12H),
3,3,6,6,9,9,12,12-Octaisopropyl-3,6,9,12-tetragermatetra-deca-
7.44–7.37 (m, 18H), 2.60 (s, 2H); 13C NMR (126 MHz, CDCl3) 1,4,7,10,13-pentayne (3b). Ethylmagnesium bromide (0.97 M
δ 133.8, 133.7, 133.3, 133.2, 130.1, 130.1, 128.6, 128.5, 107.8, in THF, 12.76 mL, 12.38 mmol) was added dropwise to a
107.4, 95.3, 82.6; LRMS (ESI, M = C44H32Ge3) m/z = 801 stirred solution of 2b (7.11 g, 12.38 mmol) in THF (123 mL) at
[M + Na]+; Anal. Calcd for C44H32Ge3: C, 67.87; H, 4.14. Found: −78 °C under a nitrogen atmosphere. The reaction mixture
C, 67.69, H, 3.97.
was stirred for 1 h at the same temperature, then the reaction
Bis((ethynyldiisopropylgermyl)ethynyl)diisopropylgermane mixture was warmed up to ambient temperature and stirred
(2b). n-Butyllithium (1.63 M in hexane, 9.04 mL, 14.73 mmol) for 2 h. The reaction mixture was cooled down to −78 °C and
was added dropwise to a stirred solution of diethynyldiiso- dichlorodiisopropylgermane9 (2.58 g, 11.23 mmol) was added.
propylgermane 1b9 (3.07 g, 14.73 mmol) in THF (150 mL) at The reaction mixture was again warmed up to ambient temp-
−78 °C under a nitrogen atmosphere. After 2 h, dichlorodiiso- erature. After 14 h, the reaction mixture was cooled down to
propylgermane5 (1.61 g, 7.02 mmol) was added at the same 0 °C. Ethynylmagnesium bromide (0.5 M in THF, 28.13 mL,
temperature. Then the reaction mixture was warmed up to 14.07 mmol) was added to the mixture, and was stirred for 1 h
ambient temperature and stirred for 16 h. The reaction was at the same temperature. Then the mixture was warmed up to
quenched with a saturated aqueous solution of ammonium ambient temperature and stirred for 7 h. The reaction mixture
chloride at 0 °C. The resulting mixture was extracted with was quenched with
a
saturated aqueous solution of
ether, and the organic layer was washed with water and brine. ammonium chloride at 0 °C. The resulting mixture was
The combined organic layer was dried over magnesium extracted with ether and washed with brine. The combined
sulfate, and the solvent was removed in vacuo. The resulting organic layer was dried over magnesium sulfate, and the
residue was purified by silica gel column chromatography solvent was removed in vacuo. The residue was purified by
(hexane to hexane/dichloromethane = 5/1) to afford 2b (2.81 g, silica gel column chromatography (hexane/dichloromethane =
70%). Colorless oil; Rf value 0.16 (hexane); IR (NaCl, neat) νmax 20/1 to 10/1) to afford 3b (2.30 g, 27%). Colorless oil; Rf value
3292, 2944, 2865, 2032, 1463, 1005, 878, 668 cm−1 1H NMR 0.11 (hexane/dichloromethane = 10/1); IR (NaCl, neat) νmax
;
(500 MHz, CDCl3) δ 2.32 (s, 2H), 1.48–1.37 (m, 6H), 1.20–1.17 3292, 2944, 2864, 2032, 1463, 1004, 878, 668 cm−1 1H NMR
;
(m, 36H); 13C NMR (126 MHz, CDCl3) δ 107.8, 106.3, 93.9, (500 MHz, CDCl3) δ 2.32 (s, 2H), 1.47–1.36 (m, 8H), 1.20–1.17
83.5, 18.8, 18.74, 18.70, 16.7, 16.6; LRMS (ESI, M = C26H44Ge3) (m, 48H); 13C NMR (126 MHz, CDCl3) δ 108.0, 107.2, 106.2,
m/z = 597 [M + Na]+.
93.9, 83.5, 18.8, 18.8, 18.7, 18.7, 16.7, 16.6; LRMS (ESI,
3,3,6,6,9,9,12,12-Octaphenyl-3,6,9,12-tetragermatetra-deca- M = C34H58Ge4) m/z = 779 [M + Na]+.
1,4,7,10,13-pentayne (3a). Ethylmagnesium bromide (0.97 M
Synthesis of octaphenylgerma[4]pericyclyne (4a) and hexa-
in THF, 1.58 mL, 1.53 mmol) was added dropwise to a stirred decaphenylgerma[8]pericyclyne (5a) from 2a. To a stirred solu-
solution of 2a (1.19 g, 1.53 mmol) in THF (15 mL) at −78 °C tion of 2a (450 mg, 0.58 mmol) in THF (36 mL) was added
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n-butyllithium (1.60 M in hexane, 0.72 mL, 1.16 mmol) drop- m.p. 213.2–215.0 °C; IR (KBr, disc) νmax 3070, 3049, 1485,
wise at −78 °C under a nitrogen atmosphere. After 1.5 h, 1434, 1095, 736, 694 cm−1; Raman νmax 2113 cm−1 1H NMR
;
dichlorodiphenylgermane (0.12 mL, 0.58 mmol) was added (500 MHz, CDCl3) δ 7.68–7.66 (m, 40H), 7.34–7.27 (m, 60H);
dropwise over 1 h with a syringe pump at the same tempera- 13C NMR (126 MHz, CDCl3) δ 133.7, 133.4, 129.9, 128.5, 107.8;
ture, and the mixture was stirred at room temperature for 16 h. LRMS (ESI, M = C140H100Ge10) m/z = 2530 [M + Na]+. Recrystal-
The reaction was quenched with ammonium chloride satu- lization for X-ray crystallographic analysis was carried out
rated aqueous solution at 0 °C. The mixture was extracted with using dichloromethane and hexane.
dichloromethane and was washed with brine. The combined
Synthesis of decaisopropylgerma[5]pericyclyne (6b) and
organic layer was dried over magnesium sulfate, and was con- icosaisopropylgerma[10]pericyclyne (7b). To a stirred solution
centrated in vacuo. The residue was purified by silica gel of 3b (1.05 g, 1.38 mmol) in THF (280 mL) was added n-butyl-
column chromatography (hexane/dichloromethane = 4/1) and lithium (1.60 M in hexane, 1.90 mL, 3.04 mmol) dropwise at
recycling preparative HPLC to afford germa[4]pericyclyne 4a −78 °C under a nitrogen atmosphere. After 2 h, dichlorodiiso-
(70 mg, 12%) as a white powder and germa[8]pericyclyne 5a propylgermane5 (381 mg, 1.66 mmol) was added at the same
(130 mg, 23%) as a white powder.9
temperature, and the reaction mixture was warmed up gradu-
Synthesis of hexadecaisopropylgerma[8]pericyclyne (5b) ally to ambient temperature. After 40 h, the reaction was
from 2b. To a stirred solution of 2b (2.36 g, 4.11 mmol) in quenched with a saturated aqueous solution of ammonium
THF (205 mL) was added n-butyllithium (1.63 M in hexane, chloride at 0 °C. The resulting mixture was extracted with
5.04 mL, 8.22 mmol) at −78 °C under a nitrogen atmosphere. dichloromethane and washed with brine. The combined
After 2 h, 1 : 0.11 inseparable mixture of dichlorodiisopropyl- organic layer was dried over magnesium sulfate, and the
germane9 and chlorotriisopropylgermane (1.05 g, of mixture, solvent was removed in vacuo. The residue was purified by
i
4.11 mmol for Pr2GeCl2) was added at the same temperature, silica gel column chromatography (dichloromethane/hexane =
and the reaction mixture was warmed up to room temperature. 1/20 to 1/5) and recycling preparative HPLC to afford 6b
After 34 h, the reaction was quenched with saturated (31 mg, 2%) and 7b (164 mg, 13%).
ammonium chloride aqueous solution at 0 °C. The mixture
Decaisopropylgerma[5]pericyclyne (6b, CCDC: 1057092). Color-
was extracted with dichloromethane and was washed with less crystal; Rf value 0.16 (hexane/dichloromethane = 10/1);
brine. The combined organic layers were dried over mag- m.p. 74.4–76.1 °C; IR (KBr, disc) νmax 2944, 2887, 2863, 1463,
nesium sulfate, and were concentrated in vacuo. The obtained 1003, 670 cm−1; Raman νmax 2103 cm−1 1H NMR (500 MHz,
;
residue was purified by silica gel column chromatography CDCl3) δ 1.40 (sept, 10H, J = 7.5 Hz), 1.19 (d, 60H, J = 7.5 Hz);
(hexane/dichloromethane = 15/1 to 5/1) and recycling prepara- 13C NMR (126 MHz, CDCl3) δ 106.8, 19.0, 16.5; LRMS (ESI,
tive HPLC to afford 5b (653 mg, 21%) as a white powder.9
M = C40H70Ge5) m/z = 937 [M + Na]+.
Synthesis of decaphenylgerma[5]pericyclyne (6a) and icosa-
Icosaisopropylgerma[10]pericyclyne (7b, CCDC: 1057093). Color-
phenylgerma[10]pericyclyne (7a). To a stirred solution of 3a less crystal; Rf value 0.11 (hexane/dichloromethane = 10/1);
(675 mg, 0.66 mmol) in THF (32 mL) was added n-butyllithium m.p. 49.2–50.5 °C; IR (KBr, disc) νmax 2945, 2887, 2864, 1463,
(1.63 M in hexane, 0.85 mL, 1.38 mmol) dropwise at −78 °C 1006, 669 cm−1; Raman νmax 2093 cm−1 1H NMR (500 MHz,
;
under a nitrogen atmosphere. After 2 h, dichlorodiphenyl- CDCl3) δ 1.39 (sept, 20H, J = 7.5 Hz), 1.17 (d, 120H, J = 7.5 Hz);
germane (215 mg, 0.72 mmol) was added at the same tempera- 13C NMR (126 MHz, CDCl3) δ 107.2, 18.8, 16.7; LRMS (ESI,
ture, and the reaction mixture was warmed up to ambient M = C80H140Ge10) m/z = 1851 [M + Na]+.
temperature. After 46 h, the reaction was quenched with a
Diphenylbis((trimethylgermyl)ethynyl)germane (8a). n-Butyl-
saturated aqueous solution of ammonium chloride at 0 °C. lithium (1.63 M in hexane, 2.44 mL, 3.97 mmol) was added
The resulting mixture was extracted with dichloromethane and dropwise to a stirred solution of diethynyldiphenylgermane
washed with brine. The combined organic layer was dried over 1a 9 (500 mg, 1.81 mmol) in THF (18 mL) at −78 °C under a
magnesium sulfate, and the solvent was removed in vacuo. The nitrogen atmosphere. After
2 h, chlorotrimethylgermane
residue was purified by silica gel column chromatography (609 mg, 3.97 mmol) was added at the same temperature, and
(dichloromethane/hexane = 1/3 to 1/1.5) and recycling prepara- the reaction mixture was warmed up to ambient temperature
tive HPLC to afford 6a (80 mg, 10%) and 7a (90 mg, 11%).
and stirred for 8 h. The reaction was quenched with a satu-
Decaphenylgerma[5]pericyclyne (6a, CCDC: 1057090). Color- rated aqueous solution of ammonium chloride at 0 °C. The
less crystal; Rf value 0.33 (hexane/dichloromethane = 2/1); m.p. resulting mixture was extracted with ether, and the organic
271.7–273.0 °C; IR (KBr, disc) νmax 3070, 3049, 1485, 1433, layer was washed with water and brine. The combined organic
1095, 735, 695 cm−1; Raman νmax 2110 cm−1 1H NMR layer was dried over magnesium sulfate, and the solvent was
;
(500 MHz, CDCl3) δ 7.72–7.68 (m, 20H), 7.43–7.35 (m, 30H); removed in vacuo. The resulting residue was purified by silica
13C NMR (126 MHz, CDCl3) δ 133.9, 133.3, 129.9, 128.5, 107.1; gel column chromatography (hexane to hexane/dichloro-
LRMS (ESI, M = C70H50Ge5) m/z = 1277 [M + Na]+. Recrystalliza- methane = 10/1) to afford 8a (927 mg, quant.). White solid;
tion for X-ray crystallographic analysis was carried out using Rf value 0.13 (hexane/dichloromethane
=
20/1); m.p.
dichloromethane and hexane.
86.6–87.3 °C; IR (KBr, disc) νmax 3066, 3051, 2979, 2911, 2102,
1
Icosaphenylgerma[10]pericyclyne (7a, CCDC: 1057091). Color- 1483, 1430, 1240, 1092, 835 cm−1; H NMR (500 MHz, CDCl3)
less crystal; Rf value 0.16 (dichloromethane/hexane = 1/2); δ 7.69–7.67 (m, 4H), 7.40–7.38 (m, 6H), 0.40 (s, 18H); 13C NMR
11816 | Dalton Trans., 2015, 44, 11811–11818
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(126 MHz, CDCl3) δ 134.7, 133.7, 129.6, 128.3, 116.6, 103.2,
0.16; LRMS (ESI, M = C24H28Ge) m/z = 533 [M + Na]+;
Anal. Calcd for C22H28Ge3: C, 51.78; H, 5.53. Found: C, 51.61;
H, 5.52.
A. W.-M. Lee, J.-X. Shia and K.-W. Cheah, Chem. Commun.,
2004, 2420–2421; (h) W.-Y. Wong, S.-Y. Poon, J.-X. Shi and
K.-W. Cheah, J. Polym. Sci., Part A: Polym. Chem., 2006, 44,
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Chem., 1999, 201, 1–42.
Diisopropylbis((trimethylgermyl)ethynyl)germane (8b). To a
stirred solution of 1b 9 (750 mg, 3.59 mmol) in THF (35 mL)
was added n-butyllithium (1.63 M in hexane, 4.85 mL,
7.90 mmol) dropwise at −78 °C under a nitrogen atmosphere.
After 2 h, chlorotrimethylgermane (1.21 g, 7.90 mmol) was
added at the same temperature, and the reaction mixture was
warmed up to ambient temperature. After 2 h, the reaction was
quenched with a saturated aqueous solution of ammonium
chloride at 0 °C. The resulting mixture was extracted with
ether, and the organic layer was washed with water and brine.
The combined organic layers were dried over magnesium
sulfate, and the solvent was removed in vacuo. The resulting
residue was purified by silica gel column chromatography
(hexane to dichloromethane/hexane = 1/10) and recycling pre-
parative HPLC to afford 8b (1.08 g, 68%). Colorless oil; Rf value
0.14 (hexane); IR (NaCl, neat) νmax 2944, 2865, 1464, 1241,
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1004, 833, 768, 667 cm−1 1H NMR (500 MHz, CDCl3) δ 1.38
;
(sept, 2H, J = 7.5 Hz), 1.16 (d, 12H, J = 7.5 Hz), 0.34 (s, 18H);
13C NMR (126 MHz, CDCl3) δ 115.1, 104.2, 18.9, 16.7, 0.04,
0.02, 0.00; LRMS (ESI, M = C16H32Ge3) m/z = 465 [M + Na]+.
Acknowledgements
This work was supported in part by a Grant-in-Aid for Scienti-
fic Research on Innovative Areas “New Polymeric Materials
Based on Element-Blocks (no. 2401)” of MEXT (no. 15H00750
for H. T. and no. 25102531 for K. K.), CREST-JST Japan for
K. K. and the Tokuyama Science Foundation for K. T. We also
thank Profs Naoki Aratani and Hiroko Yamada (CV and DPV),
Mr Kazuo Fukuda, Ms Yoshiko Nishikawa (MS measurement),
Mr Fumio Asanoma (Elemental analysis) and Mr Shohei Katao
(X-ray crystallographic analysis) of NAIST.
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