The overcrowded borazine derivative of hexabenzotriphenylene obtained through dehydrohalogenation

Article abstract of DOI:10.1002/ejoc.201200322

Treatment of 9-chloro-9-bora-10-azaphenanthrene with potassium hexamethyldisilazide yields the borazine derivative of hexabenzotriphenylene (4). This compound, the formal trimer of 9,10-azaboraphenanthryne (6), is soluble in organic solvents and was fully

Full text of DOI:10.1002/ejoc.201200322

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FULL PAPER
DOI: 10.1002/ejoc.201200322
The Overcrowded Borazine Derivative of Hexabenzotriphenylene Obtained
through Dehydrohalogenation
Sunanda Biswas,[a] Matthias Müller,[a] Christina Tönshoff,[a] Klaus Eichele,[b]
Cäcilia Maichle-Mössmer,[b] Adrian Ruff,[a] Bernd Speiser,[a] and Holger F. Bettinger*[a]
Keywords: Boron / Elimination / Isoelectronic analogues / Conformation analysis / Polycycles
Treatment of 9-chloro-9-bora-10-azaphenanthrene with po-
tassium hexamethyldisilazide yields the borazine derivative
of hexabenzotriphenylene (4). This compound, the formal tri-
mer of 9,10-azaboraphenanthryne (6), is soluble in organic
solvents and was fully characterized. The tetramer of 6 is
formed as a byproduct in the previously described high-tem-
perature synthesis of 4.
Introduction
Isoelectronic substitution of a C=C by a B=N unit pro-
vides an attractive way of modifying the properties of aro-
matic hydrocarbons because the molecular shapes are not
altered.[1] This research was pioneered by Michael Dewar,
who described the synthesis of 9-aza-10-boraphenanthrene
in 1958, and subsequently investigated the properties of
BN-substituted naphthalenes, phenanthrenes, and tri-
phenylenes.[2] Notable recent achievements are, among
others, the synthesis of a BN-pyrene by the Piers group,[3]
and advances in the chemistry of 1,2-dihydro-1,2-azabor-
ines.[4,5] The substitution of one entire benzene core of a
fully benzenoid hydrocarbon by a borazine unit is limited
to triphenylene (1) and hexabenzotriphenylene (2). Their
(BN)3 derivatives 3 and 4 were described first by Dewar et
al.[2c,2d] and by Köster et al.,[6] respectively.
be regarded cyclic iminoboranes, and these are highly reac-
tive and undergo cyclotrimerization to the corresponding
borazines.[11] Can the synthesis of 4 be achieved by em-
ploying – at least in a formal sense – the BN-aryne 6?
Not much is known about the properties of 4 because it
was reported to be insoluble in common organic solvents.[6]
It was thus characterized by MS and IR spectroscopy,[6]
and its propeller-like structure was later determined by
single-crystal X-ray diffraction.[7] The isostructural, over-
crowded hydrocarbon 2 has proven to be difficult to synthe-
size and characterize.[8,9] The most convenient and high-
yielding synthesis is the palladium-catalyzed cyclotrimeriz-
ation of 9,10-phenanthryne 5.[9] Interestingly, Köster recog-
nized that his borazine derivative 4 is a trimer of 9,10-aza-
boraphenanthryne (6), which is the BN analogue of aryne
5.[6] BN-arynes or 1,2-azaborines,[10] such as monomer 6,
One way of generating arynes, base-induced dehydro-
have never been detected or trapped previously. They can halogenation,[12] has occasionally been used for imino-
borane formation[13] but has not been reported before with
[a] Institut für Organische Chemie, Universität Tübingen,
Auf der Morgenstelle 18, 72076 Tübingen, Germany
Fax: +49-7071-29-5244
cyclic aminoboranes, such as chloroborane 7a.
Here we show that base-induced elimination of HCl from
the 9-chloro-9-bora-10-azaphenanthrene (7a) or of HOTf
from the corresponding triflate 7b indeed yields the cyclo-
trimer 4 of BN-aryne 6. In contrast to the previous re-
port,[6] 4 is sufficiently soluble for full spectroscopic charac-
E-mail: holger.bettinger@uni-tuebingen.de
[b] Institut für Anorganische Chemie, Universität Tübingen,
Auf der Morgenstelle 18, 72076 Tübingen, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200322.
Eur. J. Org. Chem. 0000, 0–0
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H. F. Bettinger et al.
FULL PAPER
terization. We also show by reinvestigation of the original UV/Vis spectrum at 365 and 380 nm, respectively.[8b,14]
synthetic procedure used to generate 4 that the tetramer of These undergo hypsochromic shifts to 320 and 343 nm,
6 is formed under high temperature conditions.
respectively, in 4. The borazine derivative shows blue fluo-
rescence in solution as well as in the solid state. In solution,
the emission maximum is at 379 nm and is thus significantly
shifted to higher energies compared to 2 (480 nm in cyclo-
hexane).[14] In the solid state (Figure 2) the maximum is
only slightly shifted compared to that in solution and is
observed at 385 nm for 4.
Results and Discussion
Treatment of 7a[2a,3c] with potassium bis(trimethylsilyl)-
amide (KHMDS) under strictly anhydrous conditions pro-
duced a colorless solid, which was soluble in toluene,
dichloromethane and tetrahydrofuran (THF), after column
chromatography and recrystallization. It was identified as 4
based on MS (EI, high resolution ESI), IR, and multinu-
clear NMR spectroscopy. In the 11B NMR spectrum, a
broad singlet was observed at δ = 36 ppm, in agreement
with a hexaaryl borazine structural unit. The characteristic
strong absorption due to the ν(BN) stretching vibration of
˜
the borazine was observed at 1366 cm–1. The powder dif-
fraction pattern obtained for 4 was identical to that mea-
sured previously[7] for single crystals of 4. The yield of 4
obtained through the dehydrohalogenation route is a re-
markable 35%, and this can be improved to 43% by in situ
generation of triflate 7b instead of chloride 7a (Scheme 1).
Use of lithium 2,2,6,6-tetramethylpiperidide (LiTMP) did
not improve the yield. Lithium diisopropylamide (LDA), on
the other hand, mainly acted as a nucleophile and produced
10-diisopropylamino-9,10-azaboraphenanthrene (8).
Figure 1. UV/Vis spectrum of
4 in dichloromethane (c =
3.5ϫ10–6 molL–1).
Figure 2. Solid-state fluorescence spectrum of 4 measured at an
excitation wavelength of 319 nm (slit 5.0 nm, scan speed 20 nm/
min).
According to Peña et al.,[9b] the Pd-catalyzed cyclo-
trimerization of phenanthryne 5 initially yields a lower sym-
Scheme 1. Formation of overcrowded borazine 4.
Cyclic voltammetry showed that compound 4 undergoes metry (C2) isomer of hexabenzotriphenylene that isomerizes
a chemically irreversible oxidation above 0.60 V (CH2Cl2; to the propeller-like D3 conformer upon heating or during
v = 50 mV/s; peak potential value, see the Supporting Infor- storage at room temperature over months. Activation pa-
mation, Figure S7), whereas 2 undergoes a reversible oxi- rameters determined by NMR spectroscopy (ΔH‡
=
dation at a formal potential of 0.82 V (both potentials rela- 22.0 kcalmol–1; ΔG‡ = 26.2 kcalmol–1) could be reproduced
tive to Fc/Fc+).[14] Only a weak rereduction peak appears by semiempirical and density functional quantum chemical
at approximately –0.2 V, indicating decomposition of the treatment. In our low-temperature synthesis of 4, we did
primary oxidation product of 4 into compounds that are not observe formation of a lower symmetry conformer after
not redox-active within the potential range investigated workup. Following Peña et al.,[9b] we computed the lower
(–0.4 Ͻ E Ͻ 1.0 V, see Figure S7). As previously observed symmetry conformer and the barrier for its isomerization
for 1 and 3,[5a,15] the UV/Vis spectra of the BN derivative 4 to C3-4. All computations (AM1, B3LYP/6-31G*) indicate
resemble those of the hydrocarbon 2 (Figure 1).[8b,14] For that this process requires roughly 3 kcalmol–1 less energy
the latter, a maximum and a shoulder are observed in the than in the hexabenzotriphenylene system.
2
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The Overcrowded Borazine Derivative of Hexabenzotriphenylene
As 4 was described as being insoluble in common organic experimental structure determination, we computed the S4
solvents, we also synthesized 4 following Köster’s thermal symmetry boat conformation of 11 at the B3LYP/6-31G*
dehydrogenation route.[6] The required N,NЈ,NЈЈ-tris-(2-bi- level of theory (Figure 4). This conformation avoids steric
phenylyl)borazine (9) is readily available from 10.[16] Single congestion of the organic groups. The BN bond lengths
crystals that were suitable for X-ray crystallographic analy- alternate (1.419 and 1.507 Å) with the shorter distance in
sis were obtained by recrystallization from acetonitrile. The the BN-phenanthrene units. The computed chemical shifts
¯
compound crystallized triclinic (P1) with two molecules of (B3LYP/6-311+G**//B3LYP/6-31G*) of 4 and 11 differ by
9 and two solvent molecules in the asymmetric unit (see the less than 2 ppm. The computed nuclear quadrupole cou-
Supporting Information). The central borazine ring is pling constant CQ of 11 is smaller (3.18 vs. 3.32 MHz) and
planar and has bond parameters comparable to those of the asymmetry parameter is larger (0.43 vs. 0.32) than for
triphenyl borazine.[17] Two of the biphenyl groups are above 4, in support of a tentative assignment to a tetrazatetrabor-
and one is below the approximate plane defined by the bor- ocine.
azine core (Figure 3). The 1H NMR spectrum shows a com-
plex aromatic region brought about by hindered rotation.
Figure 4. Structure of the S4 symmetric boat conformation of tetra-
mer 11 as computed at the B3LYP/6-31G* level of theory.
Figure 3. The structure of one of the two symmetry unique mole-
cules of N,NЈ,NЈЈ-tris-(2-biphenylyl)borazine (9) in the solid state.
Hydrogen atoms and two acetonitrile molecules are omitted for
Conclusions
clarity.
We have shown that the dehydrochlorination of 10-
Thermolysis of 9 at 400–410 °C produced a resin, and
chloro-9-aza-10-boraphenanthrene using bulky KHMDS
the soluble material thus obtained showed spectroscopic
results in the formation of the overcrowded borazine 4,
properties that were identical to those reported for 4 above,
which is the borazine analogue of hexabenzotriphenylene 2.
although the purity was lower. Interestingly, an insoluble,
In contrast to previously generated compounds of this type,
almost colorless compound (11) was also isolated in 3%
this borazine is soluble in organic solvents. Its electronic
yield from the thermolysis of 9. This latter compound is a
absorption and fluorescence spectra resemble those of 2,
tetramer of 9,10-azaboraphenanthryne (6) according to
but the transitions are blueshifted, indicating a lower degree
high-resolution EI-MS. In the IR spectrum, the strong
of delocalization. The mechanism of formation of 4, either
ν(BN) stretching vibration is redshifted by 5 cm–1 to
˜
via 1,2-azaborine derivative 6 or by stepwise nucleophilic
attack of the produced amide anion on borane 7, is the
subject of ongoing investigations.
1361 cm–1 compared to 4. For 11, an isotropic shift of
37 ppm was also obtained in the solid state by MAS 11B
NMR (see Figures S23 and S24), which were identical to
that measured for 4 (δ = 37 ppm) in the solid state. The
nuclear quadrupole coupling constant CQ and asymmetry
parameter η are 3.12(1) MHz and 0.29(1) for 4, and 3.00(5)
Experimental Section
General: All experiments were performed under anhydrous condi-
tions using argon as protective gas. Anhydrous solvents (n-hexane,
toluene) were collected from a MBraun solvent purification system
(SPS), and xylene (for the synthesis of 7a) was distilled from phos-
phorus pentoxide just before use. All NMR spectra were recorded
with Bruker DRX 250 or 400 MHz spectrometers; FWHM stands
for full width at half maximum height. The spectra were referenced
to residual solvent signals (1H, 13C) and externally (11B: BF3·OEt2).
In the case of [D2]-1,1,2,2-tetrachloroethane (C2D2Cl4), NMR
spectra were locked with CD2Cl2 and referenced to δ = 5.91 ppm
MHz and 0.40(5) for 11, respectively. This may be com-
pared to data (CQ = 3.09Ϯ0.03 MHz, η = 0.18Ϯ0.04) re-
ported previously for B-triphenylborazine.[18] Tetramers of
iminoboranes generally feature an eight-membered tetraza-
tetraborocine ring. Available solid-state structures show that
these eight-membered rings have boat conformations with
alternating BN single and double bonds.[19] Octaorganyl
tetrazatetraborocines have 11B NMR chemical shifts similar
to those of borazines.[19b] Consequently, 11 most likely also
features this structural motif. Lacking a suitable crystal for later. The NMR spectra were measured in CD2Cl2 and [D2]-
Eur. J. Org. Chem. 0000, 0–0
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H. F. Bettinger et al.
CD Cl ): δ = 36.1 ppm. IR (KBr): ν = 3440 (w), 3060 (m), 1601
(m), 1578 (m), 1555 (m), 1482 (m), 1445 (m), 1366 [vs. (νBN)], 1319
(m), 1294 (m), 1264 (m), 1163 (m), 1043 (m), 785 (m), 761 (s), 735
(s), 687 (m) cm–1. UV/Vis (CH2Cl2, 3.5ϫ10–6 molL–1): λmax (logε)
= 343 (4.212), 320 (4.701), 293 (4.599), 278 (4.656), 254 (4.833) nm.
MS (EI, 70 eV): m/z (%) = 531 [M+] (95), 525 (18), 514 (17), 263
(94), 257 (100), 249 (53), 244 (26), 237 (6), 171 (15). HRMS (ESI):
calcd. for C36H24B3N3 [M + H+] 532.234104; found 532.229585;
calcd. for [M + CH3OH + H+] 564.2589654; found 564.255179.
FULL PAPER
1,1,2,2-tetrachloroethane (purchased from Deutero GmbH and
ABCR, respectively). KHMDS, LDA (1.8 m in ethylbenzene/THF/
heptanes), borane–triethylamine complex (Sigma–Aldrich) and 2-
aminobiphenyl (Acros) were purchased and used as received. Silver
triflate was purchased from Fluka and heated to 40 °C under
vacuum prior to use. LiTMP was synthesized in situ from 2,2,6,6-
tetramethylpiperidine and nBuLi (1.6 m in hexanes) as described
earlier.[20]
˜
2
2
Electrochemical Investigations: Cyclic voltammograms were mea-
sured with an Autolab PGSTAT 100 (Metrohm, Germany) in
dichloromethane/0.1 m Bu4NPF6 as electrolyte. The reference,
working, and counter electrodes were Ag/AgClO4 0.01 m in
CH3CN/0.1 m Bu4NPF6 (Haber–Luggin double reference sys-
tem[21]), Pt disk (A = 0.067Ϯ0.001 cm2), and Pt wire (diameter:
1 mm), respectively. The solvent CH2Cl2 was predried with CaCl2,
distilled from P2O5 and K2CO3, and stored over activated basic
alumina. Bu4NPF6 was synthesized according to Dümmling et
al.[22]
11B Solid-State NMR Spectroscopy: Powdered samples of 4 and 11
were packed in 4 mm o.d. zirconia rotors and transferred into a
double bearing magic angle spinning (MAS) probe head. 11B MAS
NMR experiments were carried out at 4.7 T with a Bruker DSX-
200 NMR spectrometer operating at 200.13 (1H) and 64.209 MHz
(11B). 11B free-induction decays were acquired under MAS at a
spinning rate of 10 kHz using a one-pulse sequence of 1 μs pulse
width, corresponding to a 25° flip angle, a recycle delay of 4 s, and
high-power proton decoupling during acquisition. Chemical shifts
are referenced to the primary standard BF3·OEt2 using solid
NaBH4 as secondary reference at δ = –42.06 ppm.[23]
Spectroscopic simulations of the second-order broadened 11B cen-
tral transition[24] were carried out by using WSolids1,[25] a software
package that incorporates the space-tiling algorithm of Alderman
et al.[26] Experimental 11B MAS NMR spectra contain a strong
background signal arising from boron nitride ceramics in the probe
head, which was identified easily by obtaining 11B MAS spectra for
an empty rotor. The background signal has been included in the
simulation phenomenologically using a chemical shift anisotropy
static powder pattern.
Generation of Triflate 7b: The triflate synthesis was carried out in
the dark. Chloride 7a (0.085 g, 0.398 mmol) was dissolved in n-
hexane (30 mL) in a 100 mL Schlenk flask, and silver triflate (Ag-
OTf) (0.105 g, 0.410 mmol, 1.03 equiv.), dissolved in toluene
(2 mL), was added at 0 °C under an argon atmosphere. Immediate
formation of a white precipitate was observed. After complete ad-
dition of silver triflate solution, the reaction mixture was stirred
for 4 h at room temp. The white precipitate was removed by fil-
tration and the filtrate containing 7b was used for the next step as
described for the dehydrochlorination of 7a.
Synthesis of 8: LDA (1.8 m in THF/heptane/ethylbenzene,
0.191 mL, 0.344 mmol, 1.05 equiv.) was added to a solution of
chloride 6a (0.07 g, 0.328 mmol) in n-hexane (10 mL) at –50 °C.
The colorless suspension became faint yellow within a few minutes.
Upon slow warming to room temperature, the reaction mixture
became slightly brown and a precipitate formed. The volatiles were
removed under vacuum to leave a brown solid. Compound 8 was
sublimed at 65 °C/10–3 mbar as a colorless solid; yield 0.031 g
(34%). 1H NMR (400 MHz, CD2Cl2): δ = 8.26 (d, 3JH,H = 8.12 Hz,
3
3
1 H), 8.15 (d, JH,H = 7.72 Hz, 1 H), 8.06 (d, JH,H = 7.76 Hz, 1
H), 7.56 (t, 3JH,H = 8.32 Hz, 1 H), 7.38–7.35 (m, 1 H), 7.26 (t, 3JH,H
= 8.18 Hz, 1 H), 6.98 (t, JH,H = 7.76 Hz, 2 H), 6.36 (br. s, 1 H),
3
3
3
4.02 (heptet, JH,H = 6.84 Hz, 2 H), 1.39 (d, JH,H = 6.84 Hz, 12
H) ppm. 13C{1H} NMR (151 MHz, CD2Cl2): δ = 141.0, 140.7,
134.0, 129.6, 128.5, 125.7, 124.0, 123.1, 121.5, 119.2, 117.8, 46.9,
24.0 ppm, carbon adjacent to the boron center not observed.
11B{1H} NMR (80 MHz, CD2Cl2): δ = 28.4 ppm. MS (EI, 70 eV):
m/z = 278 [M+·], 263, 221, 178, 151. HRMS (EI, 70 eV): calcd. for
C18H23BN2 [M+·] 278.195430; found 278.19579.
Computational Details: The geometries were computed by using the
B3LYP[27] hybrid density functional method as implemented in
Gaussian 09[28] in conjunction with the 6-31G* basis set. The chem-
ical shifts were computed by using the GIAO[29] method at the
B3LYP/6-311+G**//B3LYP/6-31G* level. The electric field gradi-
ent was computed at the B3LYP/6-311+G**//B3LYP/6-31G* level
of theory (keyword: pop = efg). EFGShield[30] was used to extract
and calculate nuclear quadrupole coupling constants from
Gaussian output files.
Synthesis and Characterization of 9: Synthesized according to
Köster et al.[16] 2-Aminobiphenyl (25.76 g, 154 mmol) and triethyl-
amminborane (22.4 mL, 152 mmol) were heated to 205 °C for
6.5 h. During that period, triethylamine was released. The mixture
was brought to 160 °C and unreacted triethylamminborane was re-
moved in vacuo. A colorless solid was obtained in 80% yield after
recrystallization from acetonitrile. Crystals that were suitable for
X-ray analysis were also obtained by recrystallization from acetoni-
trile. M.p. 185 °C. 1H NMR (600 MHz, C2D2Cl4, 298 K): δ = 5.97–
7.32 (m, 27 H, Ar-H), 4.07–4.38 (br. s, 3 H, BH), 1.91 (s, 3 H,
CH3CN) ppm. 1H NMR (600 MHz, C2D2Cl4, 353 K): δ = 6.65–
7.32 (m, 27 H, Ar-H), 4.23 (br. s, 3 H, BH), 1.91 (s, 3 H,
CH3CN) ppm. 1H NMR (600 MHz, C2D2Cl4, 383 K): δ = 6.62–
7.31 (m, 27 H, Ar-H), 4.27 (br. s, 3 H, BH), 1.91 (s, 3 H,
Synthesis of 4: To a solution of chloride 6a (0.085 g, 0.398 mmol)
in n-hexane (75 mL) at –50 °C was added KHMDS (0.88 mL, 0.5 m
in toluene). The brown solid that formed overnight was isolated by
filtration under air and washed extensively with toluene
(5ϫ20 mL). After removal of toluene, the remaining solid was
treated with acetone followed by centrifugation (three times) pro-
ducing 4 as a fine colorless powder, yield 0.025 g (35%); further
purification can be achieved by column chromatography on silica
gel (CH2Cl2, Rf = 0.79); m.p. 401 °C. 1H NMR (400 MHz,
1
CH3CN) ppm. H{11B} NMR (250 MHz, CD2Cl2): δ = 6.13–7.42
(m, 27 H, Ar-H), 4.13–4.57 (br. s, 3 H, BH), 1.97 (s, CH3CN) ppm.
13C{1H} NMR (101 MHz, CD2Cl2): δ = 145.8, 144.7, 138.2, 138.0,
131.4, 130.9, 130.7, 128.7, 128.3, 127.0, 125.8 ppm. 11B{1H} NMR
(80 MHz, CD2Cl2): δ = 32.5 (br. s, 674 Hz FWHM) ppm. 11B
NMR (80 MHz, CD2Cl2): δ = 33.0 (no coupling) ppm. IR (KBr):
3
4
CD2Cl2): δ = 8.26 (dd, JH,H = 8.08, JH,H = 1.52 Hz, 1 H), 8.25
3
3
4
(d, JH,H = 8.08 Hz, 1 H), 7.63 (dd, JH,H = 8.32, JH,H = 1.02 Hz,
3
4
1 H), 7.61 (m, 1 H), 7.50 (dd, JH,H = 7.68, JH,H = 0.88 Hz, 1 H),
7.32 (m, 1 H), 7.16 (m, 1 H), 7.10 (m, 1 H) ppm. 13C{1H} NMR 1450 (sh), 1428 (vs), 1404 (vs), 1297 (w), 1191 (w), 869 (m), 772 (s),
(101 MHz, CD2Cl2): δ = 141.1, 140.7, 134.7, 131.8, 127.5, 127.3,
762 (m), 748 (m), 738 (m), 700 (s), 555 (w) cm–1. MS (EI, 70 eV):
126.3, 126.2, 125.2, 123.7, 123.6 ppm. 11B{1H} NMR (80 MHz, m/z = 537 [M+·], 536 [(M – H)+·].
ν = 3056 (m), 3023 (m), 2565 (m), 2500 (m), 1502 (w), 1479 (s),
˜
4
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The Overcrowded Borazine Derivative of Hexabenzotriphenylene
Synthesis and Isolation of 11: Obtained following the procedure[6]
described for the thermal preparation of 4 starting from the
N,NЈ,NЈЈ-tris(biphenylyl)borazine 9 (1.850 g, 3.44 mmol). After
18 h at 405 °C, a brown tar formed after cooling (eventually crys-
tals could be gathered from the surface), which was suspended in
toluene (20 mL) and sonicated for 1 h. After centrifugation, the
supernatant brown solution was discarded and fresh solvent was
added. This procedure was repeated twice, until the toluene re-
mained colorless. The residue was air-dried and then the dark solid
layer on the centrifugate was removed mechanically. A slightly yel-
low powder remained that was treated with dichloromethane and
centrifuged. As before, the supernatant solution was removed and
fresh solvent was added. After four cycles, the product was gained
as an off-white powder. During the work-up procedure some of the
product was lost; yield 67.9 mg (3%); m.p. above 410 °C. IR (KBr):
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ν = 3060 (w), 3023 (w), 1604 (m), 1577 (w), 1554 (w), 1515 (m),
˜
1484 (s), 1446 (m), 1361 (vs, νBN), 1329 (s), 1309 (s), 1261 (m), 1243
(m), 751 (s), 723 (m) cm–1. HRMS (EI, 70 eV): calcd. for
C48H32B4N4 708.29991; found 708.29892.
X-ray Crystallographic Analysis of 9: Data collection was carried
out with a STOE IPDS II diffractometer; cell determination was
carried out with 23263 reflections using X-AREA. The H atoms
were positioned geometrically (C–H = 0.93 Å for Csp2) and treated
as riding on their respective C atom, with Uiso(H) set at 1.2
Ueq(Csp2). Structure solution and refinement used SHELXS97 and
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weighted R-factor wR and goodness of fit S are based on F2, con-
[6]
ventional R-factors R are based on F, with F set to zero for negative
2
¯
F . The crystal data are as follows: triclinic; P1; a = 13.0889(11) Å,
b = 13.3034(12) Å; c = 19.1219(17) Å, α = 98.293(7)°, β =
95.924(7)°, γ = 94.973(7)°; V = 3259.7(5) Å3; Z = 4; calculated den-
sity 1.178 Mg/m3; R1 = 0.0783, wR2 = 0.1457, R1 = 0.0606
[IϾ2σ(I)]. Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-846154.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Supporting Information (see footnote on the first page of this arti-
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Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
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fellowship. A. R. thanks the Universität Tübingen for an LGFG
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Received: March 15, 2012
Published Online: ᭿
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Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20322
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Date: 28-06-12 10:06:32
Pages: 7
The Overcrowded Borazine Derivative of Hexabenzotriphenylene
Isoelectronic Polycycles
10-Chloro-9-aza-10-boraphenanthrene re-
acts with bulky base potassium hexa-
methyldisilazide by cyclotrimerization and
HCl elimination to form the overcrowded
borazine; reaction with lithium diisoprop-
ylamide results in nucleophilic substitution
of chloride by diisopropylamide. The
borazine analogue of hexabenzotriphen-
ylene was characterized spectroscopically.
S. Biswas, M. Müller, C. Tönshoff,
K. Eichele, C. Maichle-Mössmer, A. Ruff,
B. Speiser, H. F. Bettinger* ............... 1–7
The Overcrowded Borazine Derivative of
Hexabenzotriphenylene Obtained through
Dehydrohalogenation
Keywords: Boron / Elimination / Isoelec-
tronic analogues / Conformation analysis /
Polycycles
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7