Synthesis and characterization of germa[n]pericyclynes

Article abstract of DOI:10.1039/c4dt00574k

The synthesis and characterization of novel pericyclynes comprising germanium atoms and acetylenes, germa[n]pericyclynes, are described. The prepared germa[4]-, [6]-, and [8]pericyclynes were compared by ¹³C NMR spectroscopy, X-ray crystallogra

Full text of DOI:10.1039/c4dt00574k

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Synthesis and characterization of
germa[n]pericyclynes†
Hiroki Tanimoto,a Tomohiko Nagao,a Yasuhiro Nishiyama,a Tsumoru Morimoto,a
Fumiyasu Iseda,a Yuko Nagato,a Toshimasa Suzuka,b Ken Tsutsumi*c and
Kiyomi Kakiuchi*a
Cite this: Dalton Trans., 2014, 43,
8338
Received 24th February 2014,
Accepted 20th March 2014
The synthesis and characterization of novel pericyclynes comprising germanium atoms and acetylenes,
germa[n]pericyclynes, are described. The prepared germa[4]-, [6]-, and [8]pericyclynes were compared
by 13C NMR spectroscopy, X-ray crystallography, cyclic voltammetry, UV-visible spectroscopy, fluor-
escence emission spectroscopy, Raman spectroscopy, and density functional theory calculation analyses.
DOI: 10.1039/c4dt00574k
www.rsc.org/dalton
cross-hyperconjugation between skipped alkynes has been
recently focused as unexplored orbital interactions, and its
Introduction
‘[N]pericyclynes,’ as named by Scott et al., are cyclic com- strength can be tuned by the choice of element X in Fig. 1.7
pounds composed of n acetylenic units on each side of Hence, pericyclynes may display unique electrical and photo-
the ring (Fig. 1).1,2 Acyclic oligoalkynes or skipped-polyynes chemical properties, and are expected to emerge as novel func-
([–R2X–CuC–]n) have been investigated in detail. Pericyclynes tional materials.
have also been investigated because of their unique electronic
To date, various analogues have been reported in both
properties.3 In particular, their strained structures due to synthetic8–10 and theoretical studies.11 Owing to the difficulty
reduced bond angles of vertexes may reinforce the through- in their syntheses arising from strains, silapericyclynes (Si),9
space interaction between adjacent but non-conjugated with larger heteroatom vertexes than carbopericyclynes (C),2,8
alkynes.4,5 In contrast, acyclic skipped polyynes exhibit no con- have been reported with extended pericyclynes (conjugated
ductivity or very small through-space interactions.6 Moreover, polyynes on their sides).12 Changing the vertex atoms to
reduce the ring strains and bond angles may lead to the
efficient synthesis of pericyclynes and facilitate the through-
space interactions of alkynes. Phosphapericyclynes (P) have
also been reported.10 Group 14 elements seem to be efficient
because of their stability and ease of handling. However, only
carbon and silicon have been studied among Group 14
elements. In addition, the physical properties of pericyclynes
have been rarely reported. Therefore, further studies on the
other vertex atoms in terms of the ring strain and bond angles
Fig. 1 Pericyclynes.
are strongly desired. Additionally, it is also possible that chan-
ging the vertex atoms in pericyclynes can tune the conjugation
between skipped polyynes, and their properties should be
investigated.7 Herein, we report the synthesis and characteri-
zation of novel germa[n]pericyclynes, containing germanium,
a Group 14 element, on their vertexes.
aGraduate School of Materials Science, Nara Institute of Science and Technology
(NAIST), 8916-5 Takayamacho, Ikoma, Nara 630-0192, Japan.
E-mail: kakiuchi@ms.naist.jp; Fax: +81 743 72 6089; Tel: +81 743 72 6085
bDepartment of Chemistry, University of the Ryukyus, Nishihara, Okinawa 903-0213,
Japan
cDepartment of Applied Chemistry, Faculty of Engineering, Miyazaki University,
1-1 Gakuen Kibanadai-Nishi, Miyazaki 889-2155, Japan.
Results and discussion
E-mail: tsutsumi@cc.miyazaki-u.ac.jp; Fax: +81 985 58 7323; Tel: +81 985 58 7794
†Electronic supplementary information (ESI) available: The synthesis and
characterization of germapericyclynes from UV-visible, fluorescence emission
The syntheses of germa[n]pericyclynes were started with com-
mercially available diphenylgermanium dichloride 1a and
diisopropylgermanium dichloride 1b prepared from germa-
nium(IV) chloride (Scheme 1). The diethynylation of 1a–b
spectra, CV (DPV), and crystallographic data. CCDC 983323–983327. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4dt00574k
8338 | Dalton Trans., 2014, 43, 8338–8343
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indicated that the intramolecular π–π interaction between the
phenyl rings folds the molecule.
The XRD analyses showed that the bond angle of 3a was
104° for the C–Ge–C, whereas the angle was 109° for the larger
rings 4a and 4b (see the ESI† and cif data files). The bond
angles of C–X–C were almost the same as the reported values
of silapericyclynes.9f–h In contrast, the C–Ge–C bond angles of
5a and 5b varied from 104° to 108° probably because of the
low symmetry of the molecule. The angles of Ge–CuC, 3a, 4a,
and 4b, were 172°, 174°, and 174°, respectively. These values
are also the same as those of the reported sila[4]-, [6]peri-
cyclynes (173°, and 175°, respectively).9g,h The Ge–CuC bond
angles of 5a and 5b were 171–177° and 162–178° while that of
the sila[8]pericyclynes was reported to be 173°.9g,h
In terms of the bond length, all germapericyclynes showed
almost the same value (1.20–1.21 Å) for the CuC bonds; no
significant differences compared with those of silapericyclynes
(1.19 Å for [4]; 1.21 Å for [6] and [8])9g,h and acetylene (1.21 Å)9f
were found. The bond length of the Ge–C was 1.91 Å in all
compounds. The distance between the neighbouring acety-
lenes in 3a was 3.2 Å.4,5a
The Raman spectra of the powdered germapericyclynes
were located at 2107 (3a), 2114 (4a), 2112 (4b), 2099 (5a), and
2098 cm−1 (5b), whereas the reported value for silapericyclynes
was around 2135 cm−1 9e,f
.
A large difference was observed in the 13C NMR chemical
shifts of 3a. The acetylenic carbons of 3a appeared at δ
110.4 ppm; however, those for the other four germa[6]- and
[8]pericyclynes appeared at δ 107 ppm. This trend was similar
to that of the silapericyclynes.9f–h
The cyclic voltammetry (CV) showed only oxidation poten-
DPV
ox
tials obtained by differential pulse voltammetry (DPV) (E
=
1.336 (3a), 1.312 (4a), 1.320 (5a), 1.352 (4b), and 1.356 V (5b);
Fig. 2). The oxidation potentials of 4b and 5b were slightly
higher than those of the corresponding phenyl compounds.
To the best of our knowledge, this is the first example of the
CV analysis of pericyclynes.
The UV-visible spectra were recorded initially in dichloro-
methane (Fig. 3(a) and the ESI†). Two absorption maxima were
observed at 227 and 261 nm (for 3a: 227 nm (ε = 15 900),
261 nm (2375); 4a: 227 nm (17 500), 261 nm (3010); 5a: 228 nm
(19 440), 261 nm (4240), and 2a: 225 nm (3840), 261 nm (531)).
In contrast, the isopropyl derivative, 4b or 5b, did not show
specific absorption at 261 nm. Thus, the absorption at 261 nm
was derived from the benzene rings. Although 3a was highly
strained and expected to show through-space conjugations
between alkynes, only a small bathochromic shift was observed
at 227 nm according to the increase in the number of alkyne
moieties. Tykwinski et al. reported14 that the ring strains did
not affect the physical data of various analyses; our results are
in accordance with this. However, compounds 3a–5a were not
soluble in hydrocarbons; therefore, the absorptions at shorter
wavelength areas could not be investigated. However, the UV-
visible spectra of isopropyl pericyclynes 4b and 5b could be
obtained in n-hexane (Fig. 3(b) and ESI†). Two shoulders were
observed at 205 (4b: ε = 18 683, 5b: 22 377) and 213 nm (4b: ε =
Scheme 1 Synthesis and ORTEP drawings of germapericyclynes.
afforded dialkynes 2a–b. The coupling of the dianion species
of 2a–b, generated by lithiation using n-butyllithium, with 1a–
b followed by cyclization afforded phenylated germa[4]-, [6]-,
and [8]pericyclynes 3a–5a, and isopropylated germa[6]- and
[8]pericyclynes 4b and 5b. Isopropylated germa[4]-pericyclyne
3b was not observed. This is probably due to the reactivity of
2a which has reactive benzylic positions.
The germapericyclynes were obtained as crystals and ana-
lyzed by X-ray diffraction (XRD). The ring of 3a was clearly
planar; however, the analytical data of 4a showed a chair con-
formation containing a solvent molecule inside the ring, indi-
cating that germa[6]pericyclynes are promising clathrate
molecules.13 In contrast, isopropylated germa[6]pericyclyne 4b
was found to be planar. Germa[8]pericyclynes 5a and 5b
were obtained in a zig-zag form. The crystal structure of 5a
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13 919, 5b: 17 798), which were not observed in acyclic ana-
logue 2b. Because similar shoulders have been reported in the
case of silapericyclynes (204, 213, and 221 nm),9f,h these values
were assigned to the specific absorption of pericyclynes.
Similar fluorescence emission maxima were observed from
3a and 4a (λEM = 281 and 288 nm) and acyclic 2a (282 and
288 nm) (Fig. 3(c) and ESI†). In particular, 3a and 4a showed
almost the same intensity. In contrast, 5a exhibited a different
pattern. In addition to the 288 nm emission, an emission at
318 nm was observed, while the isopropyl derivative, 5b, did
not exhibit such emission. The results of UV-visible spectral
and XRD analyses showed that this emission maximum can be
attributed to the intramolecular π–π interaction of the phenyl
moiety.
To estimate the highest occupied molecular orbital
(HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of
pericyclynes, the density functional theory (DFT) calculations
of methyl-substituted pericyclynes were performed with the
B3LYP/6-31G* basis set of Gaussian 09 to compare the ring
size of the germapericyclynes and the pericyclynes containing
other Group 14 elements (Fig. 4).15 The HOMO–LUMO gap of
the germapericyclynes was larger than that of the silaperi-
cyclynes. The difference of HOMO–LUMO gaps would be sup-
ported by the result that UV absorption of pericyclyne rings
was observed at 221 nm in silapericyclynes9f,h and at 213 nm
in germapericyclynes. Among germa[4]-, [6]-, and [8]peri-
cyclynes, the smallest HOMO–LUMO gap was observed in germa-
[4]pericyclynes, and interestingly, that of germa[6]pericyclynes
was the largest. The smallest gap in germa[4]pericyclynes
would be the result of their planar ring and small C–Ge–C
angles supporting the through-space interaction between
alkynes. However, as Tykwinski et al. reported,14 these differ-
ences of gaps did not affect UV spectra. For HOMO energy
levels, the germa[4]pericyclynes was the highest, and germa[6]-
pericyclynes was the lowest. This tendency matched the results
of oxidation potentials of 3a, 4a, 5a, 4b, and 5b. The through-
space interactions between the CuC bonds were estimated in
the LUMO, even though they did not seem to enhance the
Fig. 2 Cyclic and differential pulse voltammograms of germa[n]pericy-
clynes (1.0 mM (3a, 4a, 4b, and 5b); 0.5 mM (5a) in 0.1 M n-Bu4NPF6–
CH2Cl2 solution; scan rate = 0.1 V s−1).
Fig. 3 UV-visible spectra ((a): 0.1 mM in CH2Cl2, (b): 0.1 mM in
n-hexane) and fluorescence emission spectra ((c): 0.1 mM in CH2Cl2,
λEXT = 260 nm).
Fig. 4 HOMO–LUMO gaps of pericyclynes by B3LYP/6-31G*
(Gaussian 09).
8340 | Dalton Trans., 2014, 43, 8338–8343
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physical data.5 The low symmetry of germa[8]pericyclynes was Chemical Industry, Co. Ltd), Kanto Chemical Co. Inc., and
also indicated by the HOMO orbitals.
Nakalai Tesque. Anhydrous tetrahydrofuran (THF) was pur-
chased from Kanto Chemical. Density functional theory (DFT)
calculations were performed using the Gaussian09, and the
geometries of the molecules were optimized by employing the
B3LYP density functionals and the 6-311G* basis set in this
Conclusions
We synthesized and characterized germa[4]-, [6]-, and [8]peri- series of calculations.
cyclynes comprising alternating germanium atoms and alkyne Dichlorodiisopropylgermane
(1b). Isopropylmagnesium
units. Their physical properties were evaluated by various chloride (2.0 M THF solution, 117 mL, 223 mmol) was added
spectral and XRD analyses. A small bathochromic shift of dropwise to a stirred solution of germanium(IV) chloride
germa[n]pericyclynes was found in the UV-visible spectra. The (13.6 mL, 117 mmol) in THF (233 mL) for 4 h at −78 °C under
through-space interactions were estimated by the DFT calcu- a nitrogen atmosphere, and the mixture was stirred for 13 h at
lation. Germa[4]pericyclynes were found to have the smallest the same temperature. After gradually warming up to −20 °C,
energy gap among the germapericyclynes. The cyclic voltam- the reaction was quenched with a saturated aqueous solution
metry analysis showed the oxidation potentials.
of ammonium chloride. The mixture was extracted with ether
and washed with brine. The organic layer was dried over
sodium sulfate, and the solvent was removed in vacuo (65 °C,
9 mmHg) to afford a 5 : 1 mixture of 1b and triisopropylgerma-
nium chloride as a colourless oil. The transformation to 2b
was performed without further purification to avoid decompo-
a Jeol sition. For an analytical sample, the mixture was purified
Experimental
General information
1H and 13C NMR spectra were recorded using
JNM-ECP500 spectrometer (500 MHz for 1H NMR and by recycling preparative HPLC to afford 1b (5.02 g, 19%).
125 MHz for 13C NMR). Chemical shifts are reported as IR (NaCl, neat) νmax 2954, 2869, 1465, 1388, 1226, 1008, 875,
δ values in ppm and calibrated with respect to the residual 583, 550 cm−1; H NMR (500 MHz, CDCl3) δ 1.94 (sept, 2H, J =
1
solvent peak (CDCl3, δ 7.26 for 1H NMR and δ 77.00 for 13C 7.5 Hz), 1.29 (d, 12H, J = 7.5 Hz); 13C NMR (125 MHz, CDCl3)
NMR) or tetramethylsilane (δ 0 for 1H NMR). The abbreviations δ 26.2, 17.4; LRMS (EI) m/z = 229.97 (M+).
used are as follows: s (singlet), d (doublet), t (triplet),
Diethynyldiphenylgermane (2a). Dichlorodiphenylgermane
q (quartet), sept (septet), br (broad peak), and m (complex 1a (1.0 g, 3.36 mmol) was added to a stirred ethynylmagne-
multiplet). Melting points were measured using Yanaco Micro sium bromide (0.5 M in THF, 14.8 mL, 7.39 mmol) at 0 °C
melting point apparatus. Infrared spectra were measured using under a nitrogen atmosphere. After 1 h, the reaction mixture
a Jasco FT-IR-4200 spectrometer. Mass spectra were recorded was warmed up to ambient temperature and stirred for 43 h.
using a Jeol JMS-700 MStation [EI (70 eV), CI, FAB, and ESI]. The reaction was quenched with a saturated aqueous solution
X-ray diffraction (XRD) analyses were performed using a of ammonium chloride at 0 °C. The resulting mixture was
Rigaku R-AXIS RAPID/S imaging plate diffractometer. UV/visible extracted with ether, and the organic layer was washed with
spectra were recorded using Jasco V-630. Fluorescence spectra water and brine. The organic layer was dried over magnesium
were collected using Jasco FP-6500. Raman spectra were sulfate, and the solvent was removed in vacuo. The resulting
obtained using a Jasco laser Raman spectrophotometer, residue was purified by silica gel column chromatography
NRS-2100. The cyclic voltammetry measurements of the com- (hexane) to afford 2a (874 mg, 94%) as a light pinkish crystal.
pounds were performed using a BAS electrochemical analyser Rf value 0.13 (hexane); m.p. 44.7–45.7 °C; IR (NaCl, neat) νmax
ALS612D in dichloromethane containing n-Bu4NPF6 as the 3270, 2037, 1432, 1095, 735, 694, 512 cm−1
;
1H NMR
supporting electrolyte at 298 K (100 mV s−1). The glassy carbon (500 MHz, CDCl3) δ 7.68–7.70 (m, 4H), 7.41–7.45 (m, 6H), 2.61
working electrode was polished using a BAS polishing alumina (s, 2H); 13C NMR (125 MHz, CDCl3) δ 133.6, 132.7, 130.2,
suspension and rinsed with water before use. The counter 128.6, 95.3, 82.3; LRMS (EI) m/z = 277 (M+).
electrode was a platinum wire. The measured potentials were
Diethynyldiisopropylgermane (2b). A 5 : 1 mixture of
recorded with respect to Ag/AgNO3 and normalized with dichlorodiisopropylgermane 1b and chlorotriisopropylger-
respect to Fc/Fc+. Flash column chromatography was per- mane (6.36 g of mixture, 23.8 mmol of 1b) in THF (55 mL) was
formed using Merck Silica gel 60. The progress of the reactions added dropwise to a stirred solution of ethynylmagnesium
was monitored by silica gel thin layer chromatography (TLC) bromide (0.5 M in THF, 175 mL, 87.3 mmol) in THF (55 mL)
(Merck TLC Silica gel 60 F254). The purification of the mixture for 10 min at 0 °C. After 2 h, the mixture was warmed to
of germapericyclynes was performed using a LC-908 recycling ambient temperature and stirred for 20 h. The reaction was
preparative high-performance liquid chromatograph (HPLC) quenched with a saturated aqueous solution of ammonium
equipped with a JAIGEL 2H-40 column made by Japan Analyti- chloride at 0 °C. The resulting mixture was extracted with
cal Industry Co., Ltd. Ethanol solutions of phosphomolybdic ether, and the organic layer was washed with water and brine.
acid and anisaldehyde–acetic acid–sulfuric acid were used as The organic layer was dried over magnesium sulfate, and the
the TLC stains. All the reagents were purchased from Sigma- solvent was removed in vacuo. The residue was purified by
Aldrich, Wako Pure Chemical Industries, Ltd, TCI (Tokyo silica gel column chromatography (hexane) to afford 2b
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(3.43 g, 69%) as a colourless oil. Rf value 0.35 (hexane); 10 min at −78 °C under a nitrogen atmosphere. After 2 h,
IR (NaCl, neat) νmax 3290, 2945, 2864, 2032, 1464, 669 cm−1
;
a 5 : 1 mixture of dichlorodiisopropylgermane 2b and
1H NMR (500 MHz, CDCl3) δ 2.36 (s, 2H), 1.46 (sept, 2H, J = chlorotriisopropylgermane (1.80 g of mixture, 6.49 mmol of
7.0 Hz), 1.20 (d, 12H, J = 7.0 Hz); 13C NMR (125 MHz, CDCl3) 2b) was added to the mixture at the same temperature and
δ 94.4, 82.8, 18.6, 16.4; LRMS (ESI) m/z = 232 [M + Na]+.
stirred for 18 h. The reaction mixture was warmed to 0 °C and
Synthesis of phenylated germa[n]pericyclynes (3a), (4a) and treated with a saturated aqueous solution of ammonium chlor-
(5a). n-Butyllithium (2.65 M in hexane, 2.53 mL, 6.70 mmol) ide. The mixture was extracted with dichloromethane and
was added dropwise to a stirred solution of diethynyldiphenyl- washed with brine. The organic layer was dried over mag-
germane 2a (930 mg, 3.36 mmol) in THF (17 mL) at −78 °C nesium sulfate, and the solvent was removed in vacuo. The
under a nitrogen atmosphere. After 2 h, dichlorodiphenylger- residue was purified by silica gel column chromatography
mane 1a (1.0 g, 3.36 mmol) was added at the same tempera- (dichloromethane–hexane = 1/10 to 1/4) to afford a mixture of
ture, and the reaction mixture was stirred for 41 h. The pericyclynes. Further purification was performed by recycling
reaction was quenched with a saturated aqueous solution of preparative HPLC and additional silica gel column chromato-
ammonium chloride at −78 °C and warmed up to room temp- graphy to afford dodecaisopropylgerma[6]pericyclynes 4b
erature. The resulting mixture was extracted with dichloro- (193 mg, 18%) and hexadecaisopropylgerma[8]pericyclynes 5b
methane and washed with brine. The organic layer was dried (140 mg, 13%). Both of them were obtained as a white powder.
over magnesium sulfate, and the solvent was removed
Dodecaisopropylgerma[6]pericyclyne (4b, CCDC 983326).
in vacuo. The residue was purified by silica gel column White solid; Rf value: 0.11(hexane–CH2Cl2 = 10/1); m.p.
chromatography (dichloromethane–hexane = 1/5 to 2/1) to 106.8–107.1 °C; IR (KBr, disc) νmax 2943, 2885, 2863, 1461,
1
afford a mixture of pericyclynes. The mixture was further puri- 1003, 674 cm−1; Raman νmax = 2099 cm−1; H NMR (500 MHz,
fied by recycling preparative HPLC and recrystallization CDCl3) δ 1.38 (sept, 12H, J = 7.5 Hz), 1.17 (d, 72H, J = 7.0 Hz);
(dichloromethane–methanol) to afford octaphenylgerma[4]- 13C NMR (125 MHz, CDCl3) δ 106.9, 18.9, 16.7; LRMS (ESI)
pericyclynes 3a (55 mg, 3.3%), dodecaphenylgerma[6]- m/z = 1120 [M + Na]+. Recrystallization for the XRD analysis
pericyclynes 4a (128 mg, 7.6%), and hexadecaphenylgerma[8]- was carried out using THF.
pericyclynes 5a (91 mg, 5.4%). All of them were obtained as a
hexadecaisopropylgerma[8]pericyclyne (5b, CCDC 983327).
white powder.
Colourless solid; Rf value: 0.11(hexane–CH2Cl2 = 10/1); m.p.
Octaphenylgerma[4]pericyclyne (3a, CCDC 983323). White 80.2–81.9 °C; IR (KBr, disc) νmax 2943, 2885, 2863, 1461, 1005,
powder; Rf value: 0.26 (dichloromethane–hexane = 3/10); 667 cm−1; Raman νmax = 2098 cm−1 1H NMR (500 MHz,
;
m.p. 343.0–348.0 °C; IR (KBr, disc) νmax 3070, 3023, 1484, CDCl3) δ 1.38 (sept, 16H, J = 7.5 Hz), 1.17 (d, 96H, J = 6.5 Hz);
1432, 1186, 1095, 998, 735, 695, 681, 666, 462 cm−1; Raman 13C NMR (125 MHz, CDCl3) δ 107.1, 18.8, 16.6; LRMS (ESI)
1
νmax = 2107 cm−1; H NMR (500 MHz, CDCl3) δ 7.68–7.71 (m, m/z = 1485 [M + Na]+. Recrystallization for XRD analysis was
16H), 7.37–7.44 (m, 24H); 13C NMR (125 MHz, CDCl3) δ 134.0, carried out using 1,2-dichloroethane.
132.8, 130.0, 128.4, 110.3; LRMS (ESI) m/z = 1026 [M + Na]+.
Recrystallization for XRD analysis was carried out using
1,2-dichloroethane.
Acknowledgements
Dodecaphenylgerma[6]pericyclyne (4a, CCDC 983324).
White powder; Rf value: 0.16 (dichloromethane–hexane =
This work was supported in part by a Grant-in-Aid for Scienti-
3/10); m.p. 306.7–307.5 °C; IR (KBr, disc) νmax 3071, 3051,
fic Research on Innovative Areas “New Polymeric Materials
1644, 1485, 1433, 1095, 735, 695 cm−1; Raman νmax
=
Based on Element-Blocks (no. 2401)” (25102531) of MEXT, and
CREST-JST, Japan. We are grateful to Prof. Masafumi Unno of
Gunma University for helpful advices. We also thank Profs
Daiki Kuzuhara and Hiroko Yamada (CV and DPV), Ms Yuriko
Nishiyama, Ms Yoshiko Nishikawa (HRMS measurement), and
Mr Shohei Katao (XRD analysis) of NAIST.
2114 cm−1 1H NMR (500 MHz, CDCl3) δ 7.28 (d, 24H, J =
;
7.0 Hz), 7.31–7.43 (m, 36H); 13C NMR (125 MHz, CDCl3)
δ 133.8, 133.5, 129.9, 128.4, 107.4; LRMS (ESI) m/z = 1526
[M + Na]+. Recrystallization for XRD analysis was carried out
using 1,2-dichloroethane.
Hexadecaphenylgerma[8]pericyclyne (5a, CCDC 983325).
Colourless crystal; Rf value: 0.12 (CH2Cl2–hexane = 3/10);
m.p. 252.0–253.3 °C; IR (KBr) νmax 3434, 3052, 1486, 1434,
1095, 736, 695 cm−1; Raman νmax = 2112 cm−1 1H NMR
;
Notes and references
(500 MHz, CDCl3) δ 7.67–7.70 (m, 32H), 7.30–7.39 (m, 48H);
13C NMR (125 MHz, CDCl3) δ 133.7, 133.4, 129.9, 128.5, 107.8;
LRMS (ESI) m/z = 2030 [M + Na]+. Recrystallization for the XRD
analysis was carried out using dichloromethane.
Synthesis of isopropylated germa[n]pericyclynes (4b) and
(5b). n-Butyllithium (1.60 M in hexane, 7.75 mL, 12.4 mmol)
was added dropwise to a stirred solution of diethynyldiiso-
propylgermane 2b (1.23 g, 5.90 mmol) in THF (60 mL) for
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