Arene-Inserted Extended Germa[n]pericyclynes: Synthesis, Structure, and Phosphorescence Properties

Article abstract of DOI:10.1002/chem.201701359

This report describes the synthesis and characterization of arene-inserted extended (ArEx) germa[n]pericyclynes composed of germanium and 1,4-diethynylbenzene units. These novel cyclic germanium-π unit materials were synthesized with diethynylbenzene and germanium dichloride. X-ray crystallographic analysis revealed their structures, and the planar conformation of ArEx germa[4]pericyclyne along with the regular aromatic rings. UV/Vis absorption spectra and fluorescence emission spectra showed considerably unique and highly improved character compared to previously reported germa[n]pericyclynes. Even in the absence of transition metal components, phosphorescence emissions were observed, and the emission lifetimes were dramatically improved. ArEx germa[n]pericyclynes showed high photoluminescence quantum yields, whereas low photoluminescence quantum yields were observed for acyclic compounds. Density functional theory calculations show delocalized orbitals between skipped alkyne units through a germanium tether, and an increase in the HOMO energy level, leading to a small HOMO–LUMO energy gap.

Full text of DOI:10.1002/chem.201701359

A Journal of
Accepted Article
Title: Arene-inserted Extended Germa[N]pericyclynes: Synthesis,
Structure, and Phosphorescence Properties
Authors: Hiroki Tanimoto, Junta Mori, Shunichiro Ito, Yasuhiro
Nishiyama, Tsumoru Morimoto, Kazuo Tanaka, Yoshiki
Chujo, and Kiyomi Kakiuchi
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Arene-inserted Extended Germa[N]pericyclynes: Synthesis,
Structure, and Phosphorescence Properties
Hiroki Tanimoto,*[a] Junta Mori,[a] Shunichiro Ito,[b] Yasuhiro Nishiyama,[a] Tsumoru Morimoto,[a] Kazuo
Tanaka,[b] Yoshiki Chujo,[b] and Kiyomi Kakiuchi*[a]
Dedication ((optional))
Abstract: This report describes the synthesis and characterization of
arene-inserted type extended (ArEx) germa[N]pericyclynes
composed of germanium and 1,4-diethynylbenzene units. These
novel cyclic germanium-π unit materials were synthesized with
diethynylbenzene and germanium dichloride. X-ray crystallographic
analysis revealed their structures and the planar conformation of ArEx
germa[4]pericyclyne along with the regulated aromatic rings. UV-vis
absorption spectra and fluorescence emission spectra showed
considerably unique and highly improved characters compared to
previous germapericyclynes. Even in the absence of transition metal
components, phosphorescence emissions were observed, and the
various elements for applications including electronic and optical
materials.
emission
lifetimes
were
dramatically
improved.
ArEx
germapericyclynes showed high photoluminescence quantum yields,
while that of acyclic compound was low. Density functional theory
calculations show delocalized orbitals between skipped alkyne units
through a germanium tether and an increase in the HOMO energy
level leading small HOMO-LUMO energy gap.
Introduction
Polyene and polyyne materials have been of interest of industry
and emerging high performance devices. Among them, skipped
polyyne compounds ([–M–C≡C–]n) consisting of conjugation-
interrupted alkyne units by linker atoms (M) are of particular
interest for novel optical materials.[1] Although the conjugation
degree of these compounds are limited, the use of heavy linker
atoms which influence the
d orbital can afford specific
characteristics to the materials compared to carbon (C) linkers.[2]
And to date, silicon (Si) and other main-group elements heavier
than C have been employed as linker atoms in skipped polyynes
to enhance hyperconjugation through bond and space
interactions.[3] With these backgrounds, the importance of the
“element-blocks” concept[4] has specifically increased, resulting in
novel organic-inorganic hybrid polymer functionalities by use of
Figure 1. Structure and performance improvement of germa[N]pericyclynes by
π-conjugation extension.
To improve optical properties of the skipped polyynes, cyclic
skipped polyynes, known as pericyclynes, are promising
candidates for use in functional materials such as ceramic
precursors and hole-transporting materials.[1,5] As well as
controlling the polymerization degree precisely, cyclic structures
of skipped polyynes are expected to stabilize their structures by
fixing the conformation, which could reduce thermal deactivation
of excited states. Additionally, the use of hetero or heavy linker
atoms could reinforce through-space interactions between the
skipped alkyne moieties through the double propargylic tether
units.[3,5,6] Of the group 14 atoms available for use in such systems,
we have focused on the use of germanium (Ge), which has lower
ionization energy than Si and C. By using a C(sp)–Ge σ bond
which is more stable than the C(sp)–Sn (tin) σ bond, we have
developed cyclic poly(germylene-ethynylene) compounds of
novel element-block materials which are called (extended)
[a]
Dr. Hiroki Tanimoto, Junta Mori, Dr. Yasuhiro Nishiyama, Prof. Dr.
Tsumoru Morimoto, and Prof. Dr. Kiyomi Kakiuchi
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
Shunichiro Ito, Prof. Dr. Kazuo Tanaka, and Prof. Dr. Yoshiki Chujo
Department of Polymer Chemistry
[b]
Kyoto University
Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
Supporting information for this article is given via a link at the end of
the document.
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germa[N]pericyclynes (Figure 1).[7] Structural modification of
germapericyclynes by way of expanding the alkyne unit π-
conjugation from acetylene-based (non-extended) to butadiyne-
based extended (BDEx) materials changed their various
characteristics (e.g. UV-vis, phosphorescence emission spectra
and HOMO-LUMO energy gaps) changed dramatically.[7e] This
suggests that modification of sp/sp2 conjugation units in
pericyclynes
can
further
improve the
potential
of
germapericyclynes. With this background, we designed new
extended germa[N]pericyclynes, of which arene groups are
inserted in the ring system. With the aromatic groups inside of the
ring systems, further extension of π-conjugation should improve
the optical characters of the pericyclynes. Moreover, in contrast
to the previous (extended) germa[N]pericyclynes, the arene
moiety of the pericyclyne circuits can be a good potential scaffold
for fabrication of polymeric pericyclyne materials[7d] by cross
coupling reactions, and for future performance modification by
functionalization of the arene group. In this report, we describe
the synthesis of arene-inserted extended germa[N]pericyclynes
(ArEx germa[N]pericyclynes), which are characterized by X-ray
crystallographic structures and optical performances with
comparison to those of previously synthesized (extended)
germa[N]pericyclynes.
Results and Discussion
We previously researched BDEx germapericlycnes with
peripheral phenyl groups (Figure 1).[7e] To discuss the effect of the
aryl group position (peripheral or ring component), we chose
isopropyl of alkyl group as peripheral substituents. The initial
attempt was examined by Sonogashira coupling reaction with
diethynyl germane[7a,b] and commercially available 1,4-
diiodobenzene 1 to construct ArEx pericyclyne structures.[8]
Although double cross coupling with simple iodobenzene and
diethynyl germane was successful, oligomerization/cyclization
with 1 failed to obtain the desired cyclic compounds. We believe
this was due to the difficulty of the macrocyclization between the
sp2 and the sp carbon centers. Thus, we adopted an alternative
synthetic strategy for macrocyclization by nucleophilic substitution
on Ge centers. 1,4-diethynylbenzene 3 prepared through two
steps from 1[8b] was treated with n-butyllthium and
diisopropylgermanium dichloride[7a,b] to successfully afford the
desired ArEx germa[4], [5], [6], and [7]pericyclynes 4–7. ArEx
compounds 5 and 7 of odd Ge numbers would also be afforded
by distributing substitution reaction of group 14 elements.[7c,7e,9]
Although ArEx germa[8] and [10]pericyclynes could be found from
mass spectroscopy, 4–7 were chosen for the characterization
because of the available quantity of the products for various
analyses. The desired products were purified by silica gel column
chromatography followed by recycling gel permeation
chromatography (GPC) and recrystallization. For comparison with
these cyclic compounds and acyclic monomer units 2 and 3, we
also prepared 1,4-bis(trimethylgermylethynyl)benzene 8.
Scheme 1. Synthesis of arene-inserted extended (ArEx) germa[N]pericyclynes.
The afforded ArEx germapericyclynes were crystalline
compounds, and the single crystal-obtained 4–6 were analyzed
by X-ray crystallography.[10] As shown in Figure 2, ArEx
germa[4]pericyclyne 4 exhibited a planar conformation. ArEx
germa[5]pericyclyne
5 adopted a slightly loose envelope
conformation compared to the other previous perphenyl
germa[5]pericyclynes like 9.[7b,e] Similar to the previous phenyl-
substituted acetylene-based and BDEx germa[6]periclynes,[7a,e]
Perisopropyl ArEx germa[6]pericyclyne 6 was in the chair
conformation, whereas isopropyl-substituted acetylene-based
germa[6]pericyclyne was in a nearly planar conformation.[7a,e]
Because the steric bulkiness of isopropyl group accounts for the
planar structure of the acetylene-based compound,[7a] ring
expansion should result in allowing chair conformation of 6.
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Interestingly, the benzene rings of 4 in the obtained crystal were
vertical to the pericyclyne rings, while those of 5 and 6 were
directed irregularly. In the cavities of 4 and 5, recrystallization
solvent molecules (CH2Cl2) were found. Due to the enlarged
cavity sizes from the previous molecules (for hole diagonal
distance of [4]pericyclynes, 9: 7.1 Å, 10: 10.7 Å, 4: 16.9 Å),[7] the
fixing ability by coordination seemed to be poor. The C≡C lengths
of the ArEx, BDEx, and acetylene-based germapericyclynes were
comparable (average length 4: 1.20 Å, 5: 1.19 Å, 6: 1.20 Å).[11]
The C–Ge–C angles of 4 (104.14(14)° and 103.13(14)°) were
comparable to the non-extended and BDEx [4]pericyclynes. While
those of BDEx [5]pericyclyne 11 were squeezed (102.9° average),
those of 5 were close to the non-extended compound (106°
average). In the case of 6, the C–Ge–C angles (105.6° average)
were close to the butadiyne-type compound (104.8 ° average)
and were narrower than that of acetylene-type non-extended
germa[6]pericyclyne (109° average). Ge–C≡C bonds (average
angle 4: 174°, 5: 171°, 6: 175°) were flatter than non-extended
compounds, but more bent than BDEx molecules,[11] while the Ar–
C≡C bond (average angle 4: 177°, 5: 177°, 6: 178°) are flatter
than Ge–C≡C bonds.
Figure 2. ORTEP drawings of ArEx germa[N]pericyclynes with thermal
ellipsoids at 50% probability. Hydrogen atoms are omitted for clarity; (a) ArEx
germa[4]pericyclyne 4 with dichloromethane; (b) ArEx germa[5]pericyclyne 5
with dichloromethane; (c) ArEx germa[6]pericyclyne 6; (d) Structure of
acetylene-based germa[4]pericylcyne 9, BDEx germa[4], and [5]pericyclynes 10,
11.
UV-vis spectra of ArEx pericyclynes were recorded in
dichloromethane (Figure 3a). ε values of 4–7 were much larger
than those of previous BDEx germa[N]pericyclynes such as 11
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due to the presence of alkyne-conjugated aromatic group.
Compared to the cyclic and acyclic compounds, the spectral
figures of ArEx pericyclynes seem to be similar to the end-capped
diethynylbenzene compounds 2 and 8. Although replacing the Ge
with Si did not affect the UV-vis spectra, the absorption maxima
of 4–7 (268 (sh), 282, and 298 nm) are slightly red-shifted from
those of the acyclic materials 2 and 8 (265, 278 and 293 nm). This
is probably due to the orbital interaction between neighbouring π
conjugation units through Ge tethers (See also LUMO in Figure
6). From the plot of ε values of 4–7 against the number of
diethynylbenzene units, linear correlation was observed (Figure
3b), and the degree of the increase at 298 nm is higher than those
at 282 nm. From the ORTEP figures of 4 showing vetically lying
benzene rings of 4 and irregularly lying those of 5 and 6 (Figure
2), this would be due to the increasing conjugation to enhance σ*–
π* interaction between diethynylbenzenes and Ge tethers by ring
expansion allowing rotation of benzene rings in the parallel
direction to the pericyclyne rings.
observed around 462 nm, although the intensities were lower than
those of the previous germapericyclnes (Figure 4b).[7c–e] The
relative intensity trend between 4–8 was similar to that of the
fluorescence emission around 310 nm (Figure 4a). While
phosphorescence emission results of previous BDEx and
acetylene-based germapericyclynes were obtained by excitation
of the germylbenzene (PhGe) group, excited diethynylarenes in
ArEx compounds, from which Ge atoms were placed relatively far,
can show sufficient phosphorescence emission. To our surprise,
the phosphorescence emission lifetimes of 4–7 were over 100 ms
(4: 200 ms, 5: 190 ms, 6: 130 ms, 7: 180 ms), and were much
longer than those of BDEx (ca. 0.7 ms) and acetylene-based
materials (ca. 20 µs).[7c,11] The emission of
Ge-capped
diethynylbenzene 8 was slightly shorter than those of cyclic
compounds (97 ms). The absolute photoluminescence quantum
yields ΦPL were also recorded, and 4–7 showed higher values
than 8 (ΦPL at room temperature 4: 0.13, 5: 0.24, 6: 0.19, 7: 0.14,
8: 0.043; ΦPL at 77K 4: 0.53, 5: 0.71, 6: 0.55, 7: 0.63, 8: 0.21).
Unfortunately, due to the low intensity, it was hard to observe
these phosphorescence emissions by the naked eyes. However,
These results could give us significant suggestions for the
molecular design of organic-inorganic hybrid element-block
materials with photoluminescence of a long duration.[4]
Figure 3. (a) UV-Vis spectra of the various compounds of interest in
dichloromethane. The absorption spectrum of 11 was taken from our previous
works.[7e] (b) Plot of ε values of each absorption maxima against the number of
CC-C6H4-CC units.
Figure 4. (a) Fluorescence emission spectra of ArEx germapericyclynes 4–7
and bis(trimethylgermylethynyl)benzene 8 (1×10-6 M in CH2Cl2, λex = 282 nm for
4–7, λex = 278 nm for 8). (b) Phosphorescence emission spectra (1×10-6 M in 2-
methyltetrahydrofuran at 77 K, λex = 298 mn for 4–7, λex = 293 mn for 8,
background cut off).
We next examined the fluorescence emission spectroscopy
(Figure 4). Although previous BDEx compounds like 5 only
showed very weak emission,[7e] three absorption maxima were
observed from ArEx germapericyclynes 4–7 (Figure 4a). Acyclic
compound 8 showed a considerably different emission spectrum
from other cyclic materials. Although previous germapericyclynes
consisted with acetylenes or butadiynes did not show the largely
different emission spectra from their monomeric π-components,[7]
compounds 4–7 containing arene units in the ring systems could
affect the emission spectra by interaction between skipped
diethynylbenzene units through tethering Ge moiety (See LUMO
in Figure 6 and Supporting Information). On comparing ArEx
germa[4]pericyclyne 4 to other ArEx materials 5–7, it can be seen
that emission intensity of 4 around 310 nm is relatively weak
against that around 320 nm, and the character observed from UV-
vis spectra (Figure 3a) enhanced the increasing intensity of
emission by around 310 nm compared to other emission areas.
Even in the absence of transition metal components,
phosphorescence emissions of 4–7 as well as acyclic 8 were
Similar to the previous germapericyclynes, cyclic
voltammetry (CV) and differential pulse voltammetry (DPV)
analysis of ArEx materials 4–7 indicated their oxidation potentials
(Figure 5). Those of previous BDEx germapericyclynes were
found at +1.36V and acetylene-based germapericyclynes were
from +1.31 to +1.38 V. In contrast, the ArEx germapericyclynes
4–7 had oxidation potentials at 1.50–1.69 V (4: +1.69 V, 5: +1.64
V, 6: +1.50 V, 7: +1.61 V). Although correlation between the
potential level and the ring size was not found, these new
pericyclynes showed higher oxidation potentials than previous
materials, probably due to the presence of an alkyne-conjugated
arene moiety.
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Figure 5. Cyclic and differential pulse voltammetry curves for ArEx germa[4]–
[7]pericyclynes 4–7 (0.1 mM in 0.1 M n-Bu4NPF6/CH2Cl2 solution).
To understand the molecular orbitals, and the energy levels
of these compounds and the related previous germapericyclyne
series, density functional theory (DFT) calculations were
performed (Figure 6). As observed in the previous molecules, 4
shows orbital delocalization in the LUMO between adjacent non-
conjugated alkyne moieties through the Ge vertices. This
delocalization and the presence of arene group would support the
spectral change from 8 to ArEx pericyclynes (Figure 4). Although
the LUMO energy levels are similar to 10, HOMO level of 4 is
observed at higher level than other two types of
germapericyclynes, and these follows the results from the CV.
Based on the energy level comparison of acyclic model
compounds, the small gap of 4 would be mainly derived from the
diethynylbenzene moiety. Slightly low LUMO level of 4 compared
to 12 would be one of the reasons for bathochromic shifts in UV-
vis spectra (Figure 3a). Although the energy levels and energy
gap of 12 were close to 4, low quantum yields of 8 compared to
other ArEx compounds could be attributed to a lack of Ge-(C≡
C)2 structures producing a delocalized orbital through the Ge
tether moiety. Overall, in our study of germapericyclynes starting
from 9[7a–d] to 10[7e] to this ArEx compound 4, we successfully
reduced the energy gaps, and these ArEx germapericyclynes are
presumably promising candidates of element-block optical
materials[4] which improve the performances of the previous
germapericyclynes.
Figure 6. Comparisons of the molecular orbitals and energy levels of the
(extended) germa[4]pericyclynes as determined by DFT calculations (Gaussian
09 B3LYP/6-31G(d,p)). Hydrogen atoms are omitted for clarity. The
conformation of 4 is based on CIF files from X-ray analyses. The calculated
results of 9 and 10 were obtained from our previous study. [7c,e]
.
Conclusions
Novel type of extended germapericyclynes, arene-inserted
extended (ArEx) germa[4]–[7]pericyclynes composed of
germylene-ethynylene-arene units were synthesized and were
characterized. X-ray crystallography revealed their structures and
the planar conformation of ArEx germa[4]pericyclyne along with
its regulated aromatic rings. UV-vis absorption spectra and
fluorescence emission spectra showed considerably unique and
improved characteristics compared to butadiyne-based extended
(BDEx) macrocycles. Phosphorescence emissions were clearly
observed, and the emission lifetimes were dramatically improved
over the previous germapericyclynes. Photoluminescence
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dissolved in tetrahydrofuran (101 mL), and the stirred solution was heated
at 50 °C for 21 h. The solution was filtered by Celite and was washed with
dichloromethane. The crude material obtained after concentration of the
filtrate in vacuo was purified by silica gel column chromatography (hexane
elution) to afford 2 (3.2 g, 98%) as a white solid. Rf value 0.4 (hexane);
m.p. 119–121 °C; IR (NaCl, neat) νmax 2958, 2898, 2154, 1492, 1409, 1249,
1214, 848, 757 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.39 (s, 4H), 0.24 (s,
18H); 13C NMR (126 MHz, CDCl3) δ 131.7, 123.1, 104.5, 96.3, -0.12;
HRMS (EI) calcd for C16H22Si2 (M+) 270.1260, found 270.1252.
quantum yields of ArEx germapericyclynes showed large
improvement compared to the acyclic digermyldiethynylbenzene
of the pericyclyne ring component. The molecular orbitals and
their energy levels estimated by DFT calculations show an
increase in the HOMO energy level leading to a small HOMO-
LUMO energy gap, which follow the results obtained from cyclic
and differential pulse voltammetry. These results revealed the
potential of π-extended germylene-ethynylene molecules and
provide efficient suggestions for the optical properties for further
improvement of skipped polyyne-type materials. We hope our
research leads to the optical materials of these cyclic
organogermanium element-block materials.
1,4-diethynylbenzene (3). 1,4-bis(trimethylsilylethynyl)benzene 2 (3.2 g,
12 mmol) was added to a stirred mixture of 1M potassium hydroxide
aqueous solution (36 mL), methanol (108 mL), and tetrahydrofuran (108
mL). Then, the reaction mixture was stirred for 3 h. The mixture was
extracted with dichloromethane and washed with brine. The combined
organic layer was dried over magnesium sulfate. The concentration of the
combined organic layer in vacuo was followed by silica gel column
chromatography (hexane to hexane/CH2Cl2 = 5 / 1) to afford 3 (1.2 g, 79%)
as a white solid. Rf value 0.57 (hexane / CH2Cl2 = 3 / 1); m.p. 92–95 °C;
IR (NaCl, neat) νmax 3301, 3262, 2102, 1918, 1795, 1675, 1492, 1400,
1371, 1257, 1105, 1016 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.44 (s, 4H),
3.17 (s, 2H); 13C NMR (126 MHz, CDCl3) δ 132.0, 122.5, 83.0, 79.1; HRMS
(EI) calcd for C10H6 (M+) 126.0470, found 126.0481.
Experimental Section
General Information
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 13C NMR).
The abbreviations used are as follows: s (singlet), d (doublet), sept (septet).
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
MStaion [EI (70 eV)], and Bruker Autoflex II (MALDI-TOF). UV-visible
spectra were recorded using JASCO V-630. Fluorescence emission
spectra were collected using JASCO FP-6500. Low temperature
fluorescence and phosphorescence emission spectra were recorded on a
Horiba Jobin Yvon Fluoromax-4 spectrofluorometer. Photoluminescence
quantum yields were measured using Hamamatsu Photonics Quantaurus-
QY Plus C13534-01. The cyclic voltammetry measurements of the
1,4-Bis(trimethylgermylethynyl)benzene
hexamethyldisilazide (0.48 mL, 0. 48 mmol, 1.0 M in THF) was added to a
stirred solution of 1,4-diethynylbenzene (0.14 g, 1.1 mmol) and
(8).
Lithium
3
trimethylgermanium chloride (0.38 g, 2.5 mmol) in tetrahydrofuran at -
78 °C under nitrogen atmosphere, and then the mixture was warmed up to
ambient temperature. After 4 days, the reaction was quenched with
saturated ammonium chloride aqueous solution and was extracted with
dichloromethane. The extract was washed with brine and the combined
organic layer was dried over magnesium sulfate. The organic solvent was
removed in vacuo and the obtained residue was purified by silica gel
column chromatography (hexane/ dichloromethane = 5 / 1) followed by
GPC to afford 8 (47 mg, 12%) as a white crystal. Rf value 0.11 (hexane);
m.p. 92–95 °C; IR (NaCl, neat) νmax 2975, 2912, 2154, 1495, 1414, 1236,
837, 758 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.37 (s, 4H), 0.42 (s, 18H);
13C NMR (126 MHz, CDCl3) δ 131.6, 123.1, 103.8, 96.7, -0.20; LRMS (EI,
M = C16H22Ge2) 262 (M+).
compounds were performed using
a BAS electrochemical analyser
ALS612D in dichloromethane containing n-Bu4NPF6 as the supporting
electrolyte at 298 K (100 mV s-1). The glassy carbon working electrode was
polished using BAS polishing alumina suspension and rinsed with water
before use. The counter electrode was a platinum wire. The measured
potentials were recorded with respect to Ag/AgNO3 and normalized with
respect to Fc/Fc+. All measurements of single crystal X-ray diffraction
analysis were made on a Rigaku R-AXIS RAPID diffractometer using multi-
layer mirror monochromated Mo-Kα radiation. The data were usually
collected at a temperature of -150 °C. Elemental analysis were performed
using a Perkin Elmer 2400ⅡCHNS/O. 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). Iodine on silica gel was used for the TLC stains, and TLC was
also monitored with UV lamp. The further purifications of the crude
materials were performed using a LC-908 recycling gel permeation
Synthesis of arene-inserted extended (ArEx) germa[N]pericyclynes
n-Butyllithium (23 mL, 38 mmol, 1.64 M in hexane) was added dropwise at
-78 °C to a stirred solution of 1,4-diethynylbenzene 3 (2.0 g, 15.9 mmol) in
tetrahydrofuran (317 mL) under nitrogen atmosphere. After
2 h,
diisopropylgermanium dichloride (3.65 g, 15.9 mmol), prepared in
accordance with our work,[7a] was added to the mixture dropwise. The
mixture was stirred at the same temperature for 24 h, and then warmed up
to the ambient temperature. After stirring for 6 days, the reaction was
quenched with saturated ammonium chloride aqueous solution and water
at 0 °C. The mixture was extracted with dichloromethane and was washed
with water and brine. The combined organic layer was dried over
magnesium sulfate. The organic layer was concentrated in vacuo followed
by silica gel column chromatography (hexane to hexane / CH2Cl2 = 10 / 1)
to afford crude ArEx germapericyclynes. The obtained crude material was
further purified by GPC and recrystallization to afford the ArEx germa[4],
[5], [6] and [7]pericyclynes 4–7, respectively. White crystals of the ArEx
germapericyclynes were obtained in the following yields: 4 (78 mg, 1.7 %),
5 (150 mg, 3.3%), 6 (35 mg, 0.78%), and 7 (11 mg, 0.3%).
chromatography (GPC) equipped with
a JAIGEL 2H-40 column
(chloroform elution) made by Japan Analytical Industry Co., Ltd. All the
reagents were purchased from Sigma-Aldrich, Wako Pure Chemical
Industries, Ltd, TCI (Tokyo Chemical Industry, Co. Ltd), Kanto Chemical
Co. Inc., and Merck. Anhydrous tetrahydrofuran (THF) was purchased
from Kanto Chemical. Density Functional Theory (DFT) calculations were
performed using the Gaussian 09, and the geometries of the molecules
were optimized by employing the B3LYP density functionals and the 6-
31G(d,p) basis set in this series of calculations.
1,4-Bis(trimethylsilylethynyl)benzene (2). Under nitrogen atmosphere,
1,4-diodobenzene 1 (4.0 g, 12 mmol), copper(I) iodide (0.12 g, 0.63 mmol),
and tetrakis(triphenylphosphine)palladium (0.7 g, 0.61 mmol) were
Arene-inserted extended octaisopropylgerma[4]pericyclyne (4,
CCDC 1539470). Recrystallization for X-ray analysis was performed with
dichloromethane and methanol. White solid; Rf value 0.52 (hexane /
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CH2Cl2 = 3 / 1); m.p. 250–280 °C (decomposed / discolored); IR (NaCl,
neat) νmax 2946, 2865, 2156, 1492, 1463, 1216, 1004, 835 cm-1; 1H NMR
(500 MHz, CDCl3) δ 7.42 (s, 16H), 1.55 (sept, 8H, J = 7.5 Hz), 1.28 (d,
48H, J = 7.5 Hz); 13C NMR (126 MHz, CDCl3) δ 131.9, 123.2, 106.3, 90.2,
19.0, 16.6; LRMS (MALDI-TOF, [M+Na]+, M = C60H72Ge4Na) 1155. Anal.
Calcd: C. 67.92%; H. 6.41%, found: C. 67.52%, H. 6.36%.
[1]
[2]
Acetylene Chemistry: Chemistry, Biology, and Material Science, (Eds: F.
Diederich, P. J. Stang and R. R. Tykwinski), Wiley-VCH, Weinheim, 2005.
a) M. Birot, J.-P. Pillot, J. Dunoguès, Chem. Rev. 1995, 95, 1443–1477;
b) N. J. Long, C. K. Williams, Angew. Chem., Int. Ed. 2003, 42, 2586–
2617; c) W.-Y. Wong, J. Inorg. Organomet. Polym. Mater. 2005, 15, 197–
219; d) W.-Y. Wong, Dalton Trans. 2007, 4495–4510; e) W.-Y. Wong,
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2007, 17, 189–200; f) R. Gleiter, D. B. Werz, Chem. Rev. 2010, 110,
4447–4488.
Arene-inserted extended decaisopropylgerma[5]pericyclyne (5,
CCDC 1539472). Recrystallization for X-ray analysis was performed with
dichloromethane and methanol. White solid; Rf value 0.50 (hexane /
CH2Cl2 = 3 / 1); m.p. 240–280 °C (decomposed / discolored); IR (NaCl,
neat) νmax 2942, 2862, 2157, 1494, 836, 759 cm-1; 1H NMR (500 MHz,
CDCl3) δ 7.42 (s, 20H), 1.55 (sept, 10H), 1.28 (d, 60H); 13C NMR (126 MHz,
CDCl3) δ 131.9, 123.1, 106.1, 89.7, 19.0, 16.9; LRMS (MALDI-TOF,
[M+Na]+, M =C80H90Ge5) 1438. Anal. Calcd: C. 67.92%; H. 6.41%, found:
C. 67.58%, H. 6.19%.
[3]
a) H. Sakurai, H. Sugiyama, M. Kira, J. Phys. Chem. 1990, 94, 1837–
1843; b) R. Gleiter, W. Schäfer, H. Sakurai, J. Am. Chem. Soc. 1985,
107, 3046–3050; c) R. Emanuelsson, A. Wallner, E. A. M. Ng, J. R. Smith,
D. Nauroozi, S. Ott, H. Ottosson, Angew. Chem. Int. Ed. 2013, 52, 983–
987; d) E. Göransson, R. Emanuelsson, K. Jorner, T. F. Markle, L.
Hammarström, H. Ottosson, Chem. Sci. 2013, 4, 3522–3532; e) S.
Yamaguchi, Y. Itami, K. Tamao, Organometallics 1998, 17, 4910–4916;
e) S. Yamaguchi, K. Tamao, Bull. Chem. Soc. Jpn. 1996, 69, 2327–2334.
Y. Chujo, K. Tanaka, Bull. Chem. Soc. Jpn. 2015, 88, 633–643.
For reviews of pericyclynes, see: a) L. T. Scott, K. J. M. Cooney, in:
Modern Acetylene Chemistry, (Eds: P. J. Stang and F. Diederich), VCH,
Weinheim, 1995, pp 321–351; b) A. de Meijere, S. I. Kozhushkov, in:
Carbon Rich Compounds II. Topics in Current Chemistry vol 201, (Ed. A.
de Meijere), Springer, 1999, pp 1–42; c) V. Maraval, R. Chauvin, Chem.
Rev. 2006, 106, 5317–5343.
[4]
[5]
Arene-inserted extended dodecaisopropylgerma[6]pericyclyne (6,
CCDC 1539471). Recrystallization for X-ray analysis was performed with
dichloromethane and methanol. White solid; Rf value 0.44 (hexane /
CH2Cl2 = 3/1); m.p. 250–270 °C (decomposed / discolored); IR (NaCl,
neat) νmax 2942, 2861, 2157, 1494, 1459, 1220, 1002, 836, 763 cm-1 1H
;
NMR (500 MHz, CDCl3) δ 7.42 (s, 24H), 1.56 (sept, 12H, J = 7.5 Hz), 1.27
(d, 72H, J = 7.5 Hz); 13C NMR (126 MHz, CDCl3) δ 131.9, 123.1, 106.1,
89.6, 19.0, 17.0; LRMS (MALDI-TOF, [M+Na]+, M = C96H108Ge6) 1721;
Anal. Calcd C. 67.92, H. 6.41, found C. 67.77, H.6.27.
[6]
[7]
G. Märkl, T. Zollitsch, P. Kreimeier, M. Prinzhorn, S. Reithinger, E. Eibler,
Chem.–Eur. J. 2000, 6, 3806–3820.
a) H. Tanimoto, T. Nagao, Y. Nishiyama, T. Morimoto, F. Iseda, Y.
Nagato, T. Suzuka, K. Tsutsumi, K. Kakiuchi, Dalton Trans. 2014, 43,
8338–8343; b) H. Tanimoto, T. Nagao, T. Fujiwara, Y. Nishiyama, T.
Morimoto, T. Suzuka, K. Tsutsumi, K. Kakiuchi, Dalton Trans. 2015, 44,
11811–11818; c) H. Tanimoto, T. Nagao, T. Fujiwara, T. Kakuta, K.
Tanaka, Y. Chujo, K. Kakiuchi, Polymer Chem. 2015, 6, 7495–7499; d)
H. Tanimoto, T. Nagao, S. Hosokawa, T. Fujiwara, Y. Nishiyama, T.
Morimoto, K. Tsutsumi, T. Kakuta, K. Tanaka, Y. Chujo, K. Kakiuchi,
Chem. Lett. 2016, 45, 782–784; e) H. Tanimoto, T. Fujiwara, J. Mori, T.
Nagao, Y. Nishiyama, T. Morimoto, S. Ito, K. Tanaka, Y. Chujo, K.
Kakiuchi, Dalton Trans. 2017, 46, 2281–2288.
Arene-inserted extended tetradecaisopropylgerma[7]pericyclyne (7).
White solid; Rf value 0.42 (hexane / CH2Cl2 = 3 / 1); m.p. 250–270 °C
(decomposed / discolored); IR (NaCl, neat) νmax 2942, 2861, 2157, 1494,
1220, 1006, 836, 757 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.42 (s, 28H),
1.56 (sept, 14H, J = 7.5 Hz), 1.27 (d, 84H, J = 7.5 Hz); 13C NMR (126 MHz,
CDCl3) δ 132.0, 123.2, 106.3, 89.8, 19.2, 17.0; LRMS (MALDI-TOF,
[M+Na]+, M = C112H126Ge7) 2003. Anal. Calcd: C. 67.92%; H. 6.41%,
found: C. 67.65%, H. 6.16%.
[8]
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a) J. Ohshita, D. Nada, Y. Tada, Y. Kimura, H. Yoshida, A. Kunai, Y.
Kunugi, J. Organomet. Chem. 2005, 690, 3951–3956; b) K. Yoosaf, A.
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Acknowledgements
This work was supported in part by a Grant-in-Aid for Scientific
Research on Innovative Areas ‘New Polymeric Materials Based
on Element-Blocks (No. 2401)’ of JSPS KAKENHI (JP15H00750
for H.T., JP15H00736 for K. T., JP24102013 and JP24102001 for
Y.C.). We thank Profs. Naoki Aratani and Hiroko Yamada (CV and
DPV), Mr. Shohei Katao (X-ray crystallographic analysis), Mr.
Fumio Asanoma (elemental analysis), Ms. Yoshiko Nishikawa
and Mr. Kazuo Fukuda (MS measurement) of NAIST.
R. Bortolin, B. Parbhoo S. S. D. Brown, J. Chem. Soc., Chem. Commun.
1988, 1079–1081
[10] CCDC-1539470 (4), CCDC-1539472 (5), and CCDC-1539471 (6)
contain the corresponding supplementary crystallographic data. These
data can be obtained free of charge from: The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[11] For detailed summary and comparison of values to the previous
compounds, see Supporting Information.
Keywords: germanium • pericyclynes • fluorescence emission •
phosphorescence emission • X-ray crystallographic analysis
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This report describes the syntheses of
arene-inserted type extended (ArEx)
germa[N]pericyclynes composed of
germanium-1,4-diethynylbenzene
units, and their characterization.
These novel cyclic germanium-π unit
materials were characterized by X-ray
crystallography, UV-Vis spectroscopy,
fluorescence and phosphorescence
emission spectroscopy, which showed
characteristic optical properties, and
large emission lifetimes compared to
previous derivatives.
Hiroki Tanimoto,* Junta Mori,
Shunichiro Ito, Yasuhiro Nishiyama,
Tsumoru Morimoto, Kazuo Tanaka,
Yoshiki Chujo, and Kiyomi Kakiuchi*
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Arene-inserted Extended
Germa[N]pericyclynes: Synthesis,
Structure, and Phosphorescence
Properties
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Title
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