Pentakis(phenylethynyl)benzene and hexakis(phenylethynyl)benzene: A revision concerning two far too similar prototype hydrocarbons

Article abstract of DOI:10.1002/ejoc.200300644

A previously overlooked hydrodehalogenation reaction occurring during the multiple Pd⁰-catalysed C-C coupling reaction between phenylacetylene and hexaiodo- and hexabromobenzene was found to give pentakis(phenylethynyl)- benzene ( pentatolane ) as the major product, but no hexakis-(phenylethynyl)benzene ( hexatolane ) under conditions previously claimed to yield the latter hydrocarbon. As an alternative to a viable route to hexatolane described in the literature, an independent synthesis of this hydrocarbon through sixfold Sonogashira coupling of hexakis(ethynyl)-benzene with iodobenzene has been developed. Some physical and spectroscopic properties of hexatolane and of the hitherto unknown pentatolane have been determined after thorough purification by HPLC. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200300644

FULL PAPER
Pentakis(phenylethynyl)benzene and Hexakis(phenylethynyl)benzene:
A Revision Concerning Two Far Too Similar Prototype Hydrocarbons
[a]
[a]
[a]
Jens Nierle, Dieter Barth, and Dietmar Kuck*
Keywords: Alkynes / CϪC coupling / Dehalogenation / Ethynylbenzenes / Palladium
A previously overlooked hydrodehalogenation reaction oc-
curring during the multiple Pd -catalysed C−C coupling re- through sixfold Sonogashira coupling of hexakis(ethynyl)-
erature, an independent synthesis of this hydrocarbon
0
action between phenylacetylene and hexaiodo- and hexa- benzene with iodobenzene has been developed. Some phys-
bromobenzene was found to give pentakis(phenylethynyl)-
benzene (‘‘pentatolane’’) as the major product, but no hexakis-
ical and spectroscopic properties of hexatolane and of the
hitherto unknown pentatolane have been determined after
thorough purification by HPLC.
(phenylethynyl)benzene (‘‘hexatolane’’) under conditions
previously claimed to yield the latter hydrocarbon. As an al-
ternative to a viable route to hexatolane described in the lit-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
We would like to revise and update the synthesis and the
properties of hexakis(phenylethynyl)benzene (1) and pre-
sent for the first time a synthesis and complete characteriz-
ation of its next-lower congener, pentakis(phenylethynyl)-
benzene (2). During investigations into the benzoannelation
of stilbenes and tolanes performed in the context of our
research into the synthesis of benzoannelated spheri-
[
1,2]
phanes,
we obtained data on hydrocarbon 1 that were in
conflict with reports in the literature. It turned out that, Scheme 1. Hexatolane 1 and pentatolane 2
instead of the hexafold tolane 1 claimed to be formed under
0
Pd -catalysed CϪC cross coupling conditions, the lower
congener 2, dubbed ‘‘pentatolane’’ here, was formed in their properties studied. Hexatolane- and pentatolane-
some cases and that the properties of the latter hydrocarbon based compounds are most prominent among these. As a
[
14Ϫ16]
had erroneously been ascribed to the ‘‘hexatolane’’ (1).
In view of the importance of multiply phenylethynyl-sub- cently synthesized multiple tolanes with convex-concave
novel variant of this multifaceted theme,
we have re-
[
17]
[
18]
stituted benzenes and the vast utilization of CϪC coupling and saddle-shaped molecular frameworks.
methodology in the field of material sciences, revision and
Despite the elegance of the methodologies of Sonoga-
[
19]
[20,21]
completion of our knowledge on the parent compounds 1 shira
and Heck
for performing palladium(0)-cata-
and 2 appear appropriate.
lysed ethynylation and ethenylation reactions, respectively,
The chemistry of oligo(phenylethynyl)-substituted ben- of multiply halogenated benzenes, experimental limitations
zenes has received increasing interest during recent years to the ‘‘exhaustive’’ ethenylation of adjacent ring positions
[
21,22]
owing to their extended, previously unknown π-electron of such arenes have been noted.
In general, ethynyl-
[
3,4]
systems
crystalline materials,
phenylenes
and their potential for the synthesis of liquid ation of bromo- and iodobenzenes tends to be more facile
[5Ϫ10]
[11]
dendritic structures,
and extremely large graphite cuttings far be- ation of hexaiodobenzene (4) with trimethylsilylacetylene
oligo- than ethenylation. However, the failure of a sixfold ethynyl-
[
12]
yond the coronenes.[13] Since the synthesis of hexaethynyl- under Heck coupling conditions has been reported. For-
[4]
[4]
benzene (6) by Vollhardt et al. in 1986, many derivatives tunately, use of hexabromobenzene (3) in place of 4 af-
of this interesting family of fully conjugated, rigid, quasi forded sixfold CϪC coupling, furnishing hexaethynylben-
two-dimensional hydrocarbons have been synthesized and zene 6 in satisfactory yield on subsequent desilylation.
Phenylethenylation of hexaiodobenzene (4), in contrast to
[
a]
3, was found to yield pentastyrylbenzene rather than hexa-
styrylbenzene under Heck conditions. In further accord-
Fakultät für Chemie, Universität Bielefeld,
Universitätsstraße 25, 33615 Bielefeld, Germany
[
21]
Eur. J. Org. Chem. 2004, 867Ϫ872
DOI: 10.1002/ejoc.200300644
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
867

J. Nierle, D. Barth, D. Kuck
FULL PAPER
ance with this, recent studies on hexatolane-based dendri- electron ionization (DEI) mass spectrometry, unequivocally
0
mers showed that Pd -catalysed coupling between 4 and N- confirmed the identity of the reduction product 2, a hith-
Boc-(4-ethynylphenyl)alanine methyl ester gave the corre- erto unknown hydrocarbon. Combustion analysis was also
sponding pentaethynylbenzene derivative and that hexa- performed and found to be in agreement with the structure
[
23b]
bromobenzene (3) was again required in order to furnish of 2.
Notably, analysis of the crude product mixture by
the corresponding hexatolane.[
11]
mass spectrometry on careful fractional evaporation gave
The first synthesis of the parent hexatolane 1 was de- no hint of the presence of 1, but indicated the formation of
scribed in 1987 by Praefcke et al.[ Hexabromobenzene (3) considerable amounts of a tetrakis(phenylethynyl)benzene
was treated with phenylacetylene (5) in triethylamine in the or several such isomeric ‘‘tetratolanes’’ as by-products.[
presence of palladium(0) catalyst, and a product of m.p. Repetition of the experiment with hexabromobenzene (3) in
about 310 °C (dec.) was isolated as lemon yellow needles in place of hexaiodobenzene (4) gave virtually the same re-
6]
22]
65% yield. The constitution of 1 was assigned to the prod- sults.
uct on the basis of electron ionization (EI) mass spec-
[
6]
trometry. The UV/Vis spectrum of the product showed a
1
strong absorption at λ ϭ 348 nm (ε ϭ 106000), but no H
1
3
and C NMR spectroscopic data were provided. Three
years later, the multiple CϪC cross coupling reaction be-
tween hexaiodobenzene (4) and phenylacetylene (5) under
0
Pd catalysis conditions in a triethylamine/dimethyl sulfox-
ide mixture was reported.[ The product of m.p. 169Ϫ170
22]
°
C was isolated as yellow needles and the structure of hexa-
tolane 1 was assigned to it on the basis of H NMR spectro-
1
scopic and combustion analytical data, which were also in
[
22,23]
agreement with the elemental constitution of 1.
In
1995, still another paper reported on the reaction between
hexabromobenzene (3) and phenylacetylene (5) in
N,N,NЈ,NЈ-tetramethylethylenediamine and the product of
1
m.p. 169 °C was characterized by H NMR (270 MHz) and
Scheme 2. Formation of pentatolane 2 instead of hexatolane 1
[
7]
IR spectroscopy and again claimed as hexatolane 1. The
authors also provided a UV/Vis spectrum of this product,
which appears similar but not identical to that published in
To remove any doubts about the purity of pentatolane 2,
and in view of the notorious difficulties encountered in our
987 by Praefcke.[
6,24]
1
In the course of our studies,[1] we performed the Pd0- attempts to purify hexatolane 1 (see below), we subjected
catalysed phenyethynylation of hexahalobenzenes 3 and 4 the former hydrocarbon to careful semi-preparative high-
[
6,22]
under the different previously described conditions.
In pressure liquid chromatography (HPLC). The yellow solid
one of these cases we also obtained the lower-melting prod- obtained from this purification procedure was found to
uct, the physical and spectroscopic properties of which melt at 173Ϫ174 °C, significantly above but still close to
turned out to be in conflict with those of hexatolane 1. To the melting points twice mentioned in the literature for
[
7,22]
clarify this situation, we developed an independent syn- hexatolane 1.
However, the identity of pentatolane 2
thesis of 1 and performed a careful purification and charac- was evident from the base peak at m/z ϭ 578 in its EI and
terization of the far too closely related hydrocarbons 1 DEI mass spectra, which, in line with expectation, reflects
·
ϩ
and 2.
the resistance of the molecular ion 2 towards fragmen-
[
26]
tation.
the 1Ϫ10% range only.
ecules of dihydrogen (H
along with the formation of doubly and even triply charged
Losses of H and of C H gives rise to peaks in
2 6 6
[
27]
Sequential losses of several mol-
up to 5 H ) and of (H ϩ C
Results and Discussion
2
2
2
H )
6 6
1
Pentakis(phenylethynyl)benzene (2) through C؊C Cross ions were also observed in minor relative abundances. H
Coupling Reactions with Hexahalobenzenes 3 and 4: When NMR spectra of 2 measured at 500 MHz in CDCl exhibit
3
hexaiodobenzene (4) was treated at 50 °C for 24 h in a mix- a narrow composite signal in the δ ϭ 7.33Ϫ7.38 ppm range,
ture of phenylacetylene (5), bis(triphenylphosphane)palladi- another composite signal at δ ϭ 7.57Ϫ7.83 ppm and, no-
um() dichloride, copper() iodide, DMSO and triethyl- tably, a sharp and well separated singlet at δ ϭ 7.70 ppm.
amine, fivefold CϪC coupling with concomitant single The integral ratios observed for these three resonances are
hydrodeiodination occurred, giving pentakis(phenylethynyl)- 15:10:1, in full accordance with the assumption that the
benzene (2) as the major product (Scheme 2). The material meta and para protons of pentatolane 2 are almost iso-
was isolated in 31Ϫ54% yield as a yellow solid of m.p. chronous and that magnetic deshielding of the three sets of
1
70Ϫ171 °C after repeated recrystallization. Examination ortho protons of 2 is also very similar.
1
13
Closer inspection of 2 by 1H NMR spectroscopy at
of the product by H and C NMR spectroscopy, as well
as by standard electron ionization (EI) and also by direct 600 MHz in [D ]THF revealed three doublets of doublets
8
868
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Eur. J. Org. Chem. 2004, 867Ϫ872

Pentakis(phenylethynyl)benzene and Hexakis(phenylethynyl)benzene
FULL PAPER
centred at δ ϭ 7.58, 7.61 and 7.63 in a 2:2:1 ratio, reflecting [PdCl (PPh ) ] and CuI in dimethoxyethane/triethylamine
2
3 2
three slightly magnetically different sets of ortho protons at 60 °C (Scheme 4). Flash chromatography of the product
1
3
and thus the C2v molecular symmetry of 2. The C NMR mixture again gave a yellow solid, which, in contrast to 2
spectrum (150.9 MHz) of 2 exhibits all six non-equivalent (see above), melted at 293 °C, somewhat lower than the ap-
acetylene resonances in two distinct groups at δ ϭ 86.68, proximate melting temperature published earlier.[ The
6]
8
9
6.91 and 87.03 ppm (intensity ratio ca. 1:2:2) and at δ ϭ same melting point was determined for the yellow solid iso-
5.52, 98.42 and 99.46 ppm (ca. 2:1:2). At high field, all lated by careful semi-preparative HPLC purification of the
of the six possible resonances of non-equivalent quaternary crude product mixture obtained from hexahalobenzenes 3
carbon nuclei of the pendant rings are also observable, as and 4 and phenylacetylene (5) under the reaction conditions
1
are six of the nine non-equivalent tertiary carbons at these described in the previous section. Mass spectra and H and
13
rings. The unique CH group of the central ring appears at
C NMR spectra of the hexatolane products obtained
lowest field (δ ϭ 133.80 ppm). Unlike in the lower-resolu- from these independent syntheses and purification pro-
tion NMR spectra, which reflect an apparent equivalence cedures were found to be identical.
of the five phenylethynyl groups, the formal C symmetry
2
v
1
3
of 2 is also confirmed by C NMR at high resolution. Fi-
nally, both accurate mass measurements and combustion
analysis were found to be in accordance with the elemental
composition (C H ) of pentatolane 2.
4
6
26
Hexakis(phenylethynyl)benzene (1) by Sonogashira Cross
Coupling of Hexabromo- and Hexaiodobenzene with Phenyl-
acetylene: Repetition of the sixfold CϪC coupling of hexa-
bromobenzene (3) with phenylacetylene (5) under the con-
ditions described by Praefcke et al.[ (that is, in the absence
of DMSO but in the presence of an excess of triphenylphos-
phane) was also performed several times. In accordance
with the results reported by these authors, hexatolane 1 was
found to be the major product (Scheme 3). The crude prod-
uct, obtained in 67Ϫ70% yield after a single recrystalliza-
tion, did not contain pentatolane 2 or any tetratolanes, as
6]
Scheme 4. Independent synthesis of hexatolane 1 from hexaethynyl-
benzene (6)
EI and, in particular, DEI mass spectrometry, as well as
1
1
13
found by DEI mass spectrometry and H NMR spec-
H and C NMR spectroscopy, clearly confirmed the iso-
troscopy. However, contamination with partially chlori- lation of pure hexatolane 1. In line with expectations, the
nated products was inferred from characteristic peaks above EI and DEI mass spectra of 1 exhibit the molecular ion
m/z ϭ 678. In spite of repeated attempts, recrystallization signals at m/z ϭ 678 as the base peaks, with fragmentation
[
28]
did not enable us to remove these impurities completely.
occurring only to a very minor extent. Losses of up to five
The corresponding experiments starting from hexaiodoben- H2 molecules in low relative abundances (Յ5%) and of
zene 2 furnished similar product mixtures in 70Ϫ73% C H , as well as the combined loss of H and C H (ca.
6
6
2
6
6
yields.
10% each) were observed, together with the formation of
doubly charged fragment ions in the m/z ϭ 298Ϫ300 range,
2ϩ
corresponding mainly to ions [1 Ϫ (H , C H )] (ca. 10%).
2
6
6
Triply charged ions were also generated in very minor rela-
tive abundances. Thus, not surprisingly, the gas-phase frag-
mentation behaviour of the radical cations of hexatolane
·
ϩ
·ϩ
(
1 ) and of pentatolane (5 ) is very similar.
1
The H NMR spectra (500 and 600 MHz) of 1 exhibit
only two slightly broadened singlets at δ ϭ 7.40 and 7.67,
Scheme 3. Synthesis of hexatolane 1 without formation of penta- with an integral ratio of 3:2, in accordance with 18 protons
tolane 2 under conditions described by Praefcke et al. for the case
at the meta and para positions and twelve protons at the
ortho positions of the six phenyl rings. In comparison with
the spectrum of pentatolane 2, additional magnetic de-
[
6]
of X ϭ Br
Hexakis(phenylethynyl)benzene (1) by Cross Coupling of shielding due to the presence of the sixth phenyl group in 1
Hexaethynylbenzene and Iodobenzene ؊ an Independent is almost negligible (∆δ ϭ δHi(1) Ϫ δHi(2) Յ ϩ0.05 ppm).
Synthesis: Because of the difficulties involved in obtaining
hexatolane 1 in a pure state by the published procedures, we dissolved in [D ]tetrahydrofuran
The 13C NMR spectrum (150.9 MHz) of hexatolane 1
[
28]
reflects the effective
8
attempted to synthesize this hydrocarbon in an independent (formal) D6h symmetry of the molecule in solution. It exhib-
way. To this end, hexaethynylbenzene (6), obtained from its only seven different resonances, three of them (δ ϭ
hexabromobenzene (3) via hexakis(trimethylsilylethynyl)- 128.5, 129.0 and 131.7 ppm, in an approximate intensity ra-
benzene according to the procedure published by Vollhardt tio of 2:1:2) attributable to the carbon nuclei in the tertiary
[
4]
et al., was treated with iodobenzene (7) in the presence of positions. The quaternary carbon atoms of the central ring
Eur. J. Org. Chem. 2004, 867Ϫ872
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869

J. Nierle, D. Barth, D. Kuck
FULL PAPER
Table 1. 13C chemical shifts (δ) of hexatolane 1 and pentatolane 2
Compound[a]
1
2
Position
(all)
127.39
86.79
[C-1(5)ϪCCPh]
[C-2(4)ϪCCPh]
[C-3ϪCCPh]
C-6
133.80
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
central
C
C
C
125.44
127.37
128.54
86.68
α
[b]
[b]
[b]
87.0
87.0
β
99.51
95.52
122.80
131.65
128.44 [
99.46
123.04
131.60 [
128.44
98.42
C-1Ј
122.93
131.65
128.47
129.01
123.02
131.65
128.44
128.90
b]
C-2Ј, C-6Ј
C-3Ј, C-5Ј
C-4Ј
b]
[b]
[b]
128.87
128.90
[
a]
Measured at 125.9 MHz in [D
8
]THF. [b] No more specific assignment achieved.
resonate at significantly lower field (δ ϭ 127.4 ppm) than
those of the pendant phenyl groups (δ ϭ 122.9 ppm) and
the lines for the inner (α) and outer (β) acetylene carbon
nuclei appear at δ ϭ 86.8 and δ ϭ 99.5 ppm, respectively,
as confirmed by correlation (HMQC and HMBC) measure-
ments. The acetylenic carbon atoms of hexatolane deriva-
[
11]
tives such as the dendritic phenylalanine analogues of 1
were found to resonate at similar fields but no assignment
1
3
was made. Thus, as expected, all four C resonances of the
pendant phenyl rings of 1 and 2 are found to be very similar
(Table 1). However, significant differences are found be-
tween the chemical shifts of the acetylene groups and the
central carbon atoms of 1 and some of the corresponding
β
positions of 2. The resonances of the C nuclei of 1 are Figure 1. UV/Vis spectra of hexatolane 1 and pentatolane 2
Ϫ6
Ϫ1
β
2 2
(CH Cl , 3.1 ϫ 10 mol·L )
almost identical with the resonances of those C nuclei of
2
that are incorporated in the phenylacetylene groups at C-
2
and C-4 (δ ϭ 99.5 ppm) but slightly and even drastically
β
different from those of the C nuclei present in the phenyl-
In summary, a new synthesis of hexakis(phenylethynyl)-
acetylene groups at C-3 (δ ϭ 98.4 ppm) and at C-1 and C- benzene (‘‘hexatolane’’, 1) together with careful HPLC
5
of 2 (δ ϭ 95.5 ppm), respectively. Similar differences are purification has enabled us to determine and correct the
noted for the chemical shifts of the quaternary carbon physical properties of this prototypical hydrocarbon in de-
centres in the central rings of 1 and 2 (Table 1). In turn, tail. Its syntheses from hexabromo- and hexaiodobenzene
α
0
however, the resonances of the C nuclei of 1 and 2 are all and phenylacetylene under Pd catalysis conditions, claimed
within a very small range (δ ϭ 86.7Ϫ87.0).
in the literature, were found to be incorrect or dubious. In
UV/Vis Spectra of Hexatolane (1) and Pentatolane (2): In one of the procedures, pentakis(phenylethynyl)benzene
view of the broad interest in the optical properties of the (‘‘pentatolane’’, 2) is formed instead of hexatolane as the
multiply phenylethynyl-substituted benzenes and in particu- major coupling product, together with even lower ana-
lar of the discrepancies encountered with the identity and logues. Also, purification of hexatolane 1, once obtained, is
purification of the parent hydrocarbon 1, the electronic difficult, and tedious HPLC purification has to be per-
spectra of 1 and 2 were measured (Figure 1).
formed to remove contaminants of similarly low solubility.
The UV/Vis spectrum of hexatolane (1) measured on the By employment of a complementary synthesis strategy
0
HPLC-purified material exhibits the maximum absorption using Pd cross coupling of hexaethynylbenzene and iodo-
at λ ϭ 349 nm (ε ϭ 155000) and a shoulder at λ ഠ 371 nm benzene, these complicating factors can be largely circum-
(
ε ϭ 81000). The former absorption is in good agreement vented.
with the maximum absorption published for hexatolane 1
[6]
by Praefcke et al. (λ ϭ 348) and also by Kondo et al. (λ ϭ
[
7]
Experimental Section
350 nm). It is interesting to mention that the low-energy
shoulder has also been noted (at λ ഠ 370 nm) by one of
[
7]
General: Melting points (uncorrected): Electrothermal, Melting
point apparatus. HPLC purification of compounds 1 and 2 was
performed with a MerckϪHitachi instrument equipped with an L-
these groups. The UV/Vis spectrum of pentatolane 2 exhi-
bits the maximum absorption at λ ϭ 333 nm (ε ϭ 93000)
and a shoulder at λ ഠ 368 nm (ε ϭ 36000). Notably, these
bands fit well in between those observed in the spectra of
6250 Intelligent Pump, an L-7420 UV/Vis detector and a Hibar
column packed with LiChrosorb Si 60 (Ø, 7 µm). The isocratic
hexatolane 1 and the D -symmetrical next-lower analogue,
2
h
runs (cyclohexane/CHCl , 2:1 v/v) were monitored at λ ϭ 280 nm.
3
1
,2,4,5-tetrakis(phenylethynyl)benzene,
published
by IR spectroscopy: PerkinϪElmer, Model 841. NMR spectroscopy:
[7]
1
13
Kondo et al. (λ ϭ 315 nm and λ ഠ 350 nm).
Bruker DRX 500 ( H, 500 MHz, C: 125.7) and Bruker Avance
870
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Pentakis(phenylethynyl)benzene and Hexakis(phenylethynyl)benzene
FULL PAPER
6
00 (1H, 600 MHz, 13C: 150.9 MHz). UV/Vis spectroscopy: (150.9 MHz, [D
8
]THF): δ ϭ 133.80 (t, C-6), 131.65, 131.61 and
ph,ortho
PerkinϪElmer UV Lambda 40. Mass spectrometry: Fisons VG,
Autospec; accurate mass measurements (HRMS) was performed
with use of the peak-matching method at a resolution of m/∆m ϭ
131.60 (all t, C
, rel. intensities ca. 1:2:2), 128.90 and 128.87
ph,para
(both t, C
(t, C
, rel. intensities ca. 1.5:1), 128.54 (q, C-3), 128.44
ph,meta
), 127.37 (q, C-2 and C-4), 125.44 (q, C-1 and C-5),
ph,ipso
8
2
000 (10% valley). Combustion analysis: PerkinϪElmer, Model
40.
123.04, 123.02 and 122.80 (all q, C
99.46, 98.42, 95.52 (all q, C ϵC, rel. intensities ca. 2:1:2, assign-
, rel. intensities ca. 2:1:2),
β
β(meta)
, Cβ(para),
ment based on rel. intensities and HMBC: C
β(ortho)
α
Hexakis(phenylethynyl)benzene (1): A solution of hexaethynylben-
zene (6, 40.0 mg, 0.18 mmol) in DME (10 mL), bis(triphenylphos-
phane)palladium() chloride (7.5 mg, 10 µmol), copper() iodide
C
, respectively), 87.03, 86.91, 86.68 (all q, CϵC , rel. intensit-
[
4]
13
·ϩ
2
ies 2:2:1) ppm. MS (DEI, 70 eV): m/z ϭ 580 (17) [{ C }M ], 579
1
3
·ϩ
13
·ϩ
(50) [{ C }M ], 578 (100) [{ C }M ], 577 (10) in part [M Ϫ
1
0
ϩ
·ϩ
ϩ
(1.0 mg, 5.0 µmol) and triethylamine (10 mL) was prepared, and H] , 576 (12) in part [M Ϫ H ] , 575 (8) in part [M Ϫ (H, H )] ,
2
2
·ϩ
ϩ
iodobenzene (7, 322.0 mg, 1.58 mmol) was added. The mixture was
stirred at 60 °C for 68 h under argon and then cooled to ambient
574 (10) in part [M Ϫ 2 H ] , 573 (5) in part [M Ϫ (H, 2 H )] ,
2
2
572 (6, [M Ϫ 3 H2]· ), 500 (13, [M Ϫ C H ] ), 499 (7), 498 (11),
ϩ
·ϩ
6
6
temperature. The solvent was evaporated and the residue was sub- 497 (3), 496 (4), 250 (5), 249.5 (5), 249.0 (9). UV/Vis (CH Cl ,
2
2
Ϫ6
Ϫ1
jected to flash chromatography through silica gel with CHCl
3
/n-
3.1ϫ10 mol·L ): λ (ε) ϭ 333 (93000), 368 nm (s, 36000). Accu-
hexane (1:1). Hexatolane (1, 50.0 mg, 41%) was obtained as a yel-
rate mass by EI-MS (C H ): calcd. 578.2034; found 578.2037.
4
6
26
1
low solid, m.p. 293 °C (dec.). H NMR (500 MHz, CDCl ): δ ϭ C H (578.72): calcd. C 95.47, H 4.53; found C 95.28, H 4.71.
3
46 26
Ϫ1
c c
7.67 (m , 12 H), 7.40 (m ,
, 18 H) ppm. IR (KBr): ν˜ ϭ 3055 cm
When the reaction was carried out by starting from hexabromoben-
zene (3, 1.38 g, 2.50 mmol) instead of 4 with the same components
in the same amounts and under the same conditions as described
2
926, 2855, 1598, 1493, 1067, 1024, 749, 687. MS (EI, 70 eV): m/z
13
·ϩ
13
·ϩ
(rel. int., %) ϭ 680 (18) [ C
2
]M ], 679 (57) [{ C
1
}M ], 678 (100)
, 675 (3) [M Ϫ (H,
, 599 (11), 598 (13), 597 (6), 299 (15).
12/CHCl , 2:1), the
·
ϩ
ϩ
·ϩ
2
[M ], 677 (5) [M Ϫ H] , 676 (5) [M Ϫ H ]
ϩ
·ϩ
2 2
above, recrystallization from CH Cl /EtOH furnished pentatolane
H
2 2
)] , 674 (3) [M Ϫ 2 H ]
2
in virtually the same yield (460 mg, 32%), and with identical
After purification by HPLC (silica gel, c-C
following data were obtained for 1: M.p. 293 °C (dec.). H NMR
6
H
3
1
properties.
ortho
meta
(600 MHz, [D
8
]THF): δ ϭ 7.699 (m
c
, 12 H
), 7.433 (m
c
, 18 H
para
13
and H ) ppm. C NMR, HMBC (150.9 MHz, [D
1
8
]THF): δ ϭ
ph,ortho
ph,para
ph,meta
31.65 (t, C
), 129.01 (t, C
), 128.47 (t, C
), 99.51 (q, C /C), 86.79 (q, C/
), 127.39
Acknowledgments
We are grateful to Dr. Mathias Letzel and Dr. Andreas Mix for
ph,ipso
β
(q, C-1 to C-6), 122.93 (q, C
α
13
·ϩ
C ) ppm. MS (DEI, 70 eV): m/z ϭ 680 (22) [{ C
2
}M ], 679 (59)
13
·ϩ
·ϩ
ϩ
[{ C
1
}M ], 678 (100) [M ], 677 (6) in part [M Ϫ H] , 676 (6) in their assistance in spectroscopic analyses.
·
ϩ
ϩ
part [M Ϫ H
2
ϩ
]
, 675 (5) in part [M Ϫ (H, H
2
)] , 674 (6) in part
·
ϩ
2 2
[M Ϫ 2 H ] , 673 (4) in part [M Ϫ (H, 2 H )] , 672 (5) [M Ϫ 3
·
ϩ
·ϩ
H
2
]
, 600 (14) [M Ϫ C
6
H
6
]
, 599 (11), 598 (15), 597 (7), 596 (9),
Cl , 3.1 ϫ 10 mol·L ): λ (ε) ϭ
2 2
[1] [1a]
J. Nierle, D. Kuck, in Threefold ortho-Terphenyls as Inter-
Ϫ6
Ϫ1
5
94 (3), 298 (10). UV/Vis (CH
48 (155000), 370 nm (s, 81000). Accurate mass by EI-MS
30): calcd. 678.2347; found 678.2340. C54 30 (678.84): calcd.
C 95.55, H 4.45; found C 94.43, H 4.62.
mediates to Spherical C60-Hydrocarbons, 8th International
Symposium on Novel Aromatic Compounds (ISNA-8),
Braunschweig, Germany, July 30 to August 04, 1995, Poster
No. 10. [ J. Nierle, Doctoral thesis, University of Bielefeld,
3
(C
54
H
H
1b]
1998.
[2]
For the chemistry of non-benzoannelated spheriphanes, see: J.
Groß, G. Harder, A. Siepen, J. Harren, F. Vögtle, H. Stefan,
K. Gloe, B. Ahlers, K. Cammann, K. Rissanen, Chem. Eur. J.
Pentakis(phenylethynyl)benzene (2): A mixture of hexaiodobenzene
(
(
4, 2.08 g, 2.50 mmol), phenylacetylene (5, 3.37 g, 33.0 mmol), bis-
triphenylphosphane)palladium() chloride (0.12 g, 0.17 mmol),
1
996, 2, 1585Ϫ1595, and previous papers cited therein.
copper() iodide (0.07 g, 0.37 mmol) and triethylamine (15 mL) and
DMSO (3 mL) was heated at 50 °C under argon for 24 h. The reac-
tion mixture was cooled to ambient temperature and then filtered,
and the filtrate was concentrated in vacuo to yield a yellow solid,
which was recrystallized from ethanol/dichloromethane (1:1).
[3]
[4]
J. Zhang, D. J. Pesak, J. L. Ludwick, J. S. Moore, J. Am. Chem.
Soc. 1994, 116, 4227Ϫ4239.
R. Diercks, J. C. Armstrong, R. Boese, K. P. C. Vollhardt, An-
gew. Chem. 1986, 98, 270Ϫ271; Angew. Chem. Int. Ed. Engl.
1986, 25, 268Ϫ269.
[
5] [5a]
Pentatolane 2 (0.45 g, 31%), containing some residual tetratolane(s)
M. Ebert, D. A. Jungbauer, R. Kleppinger, J. H. Wendorf,
[
5b]
1
B. Kohne, K. Praefcke, Liq. Cryst. 1989, 4, 53Ϫ67.
K.
(
(
1
see above), was obtained as a yellow solid, m.p. 170 °C. H NMR
Praefcke; B. Kohne, D. Singer, Angew. Chem. 1990, 102,
200Ϫ202; Angew. Chem. Int. Ed. Engl. 1990, 29, 177Ϫ179.
500 MHz, CDCl
3
): δ ϭ 7.70 (s, 1 H), 7.63 (m
c c
, 10 H), 7.35 (m ,
): δ ϭ 133.84 (t), 131.78
5 H) ppm. 13C NMR (125.7 MHz, CDCl
3
[
5c]
K. Praefcke, B. Kohne, D. Singer, D. Demus, G. Pelzl, S.
(
(
8
1
7
5
t), 128.81 (t),128.62 (q), 128.45 (t), 127.53 (q), 125.34 (q), 123.19
[5d]
Diele, Liq. Cryst. 1990, 7, 589Ϫ594.
D. Singer, M. Ebert, A. Liebmann, J. H. Wendorff, Liq. Cryst.
991, 10, 147Ϫ159.
K. Praefcke, B. Kohne,
q), 122.88 (q), 99.39 (q), 98.31 (q), 95.49 (q), 87.46 (q), 87.32 (q),
Ϫ1
7.09 (q). IR (KBr): ν˜ ϭ ϭ 3055 cm , 2925, 1796, 1781, 1773,
1
[
6]
701, 1596, 1492, 1442, 1407, 1145, 1067, 1025, 998, 906, 884, 757,
B. Kohne, K. Praefcke, Chimia 1987, 41, 196Ϫ198.
K. Kondo, S. Yasuda, T. Sakaguchi, M. Miya, J. Chem. Soc.,
Chem. Commun. 1995, 55Ϫ56.
1
3
·ϩ
[7]
2
48, 725, 689, 621. MS (EI, 70 eV): m/z ϭ 580 (17) [{ C }M ],
13
·ϩ
·ϩ
ϩ
79 (50) [{ C
1
}M ], 578 (100) [M ], 577 (12) [M Ϫ H] , 576 (13)
[8] [8a]
·
ϩ
ϩ
·ϩ
S. Marguet, A. Germain, P. Milli e´ , Chem. Phys. 1996, 208,
351Ϫ373. [ S. Marguet, D. Markovitsi, D. Goldmann, D.
Janietz, K. Praefcke, D. Singer, J. Chem. Soc., Faraday Trans.
[M Ϫ H
2
]
, 575 (8) [M Ϫ (H, H
2
2
)] , 574 (11) [M Ϫ 2 H ] , 573
8b]
ϩ
·ϩ
2 2
(5) [M Ϫ (H, 2 H )] , 572 (7) [M Ϫ 3 H ] , 500 (16), 498 (14),
4
96 (5), 286 (12), 249 (17). After purification by HPLC (silica gel,
c-C 12/CHCl , 2:1), the following data were obtained for 2: M.p.
73Ϫ174 °C. H NMR, HMQC, HMBC (600 MHz, [D
1
997, 93, 147Ϫ155.
C. J. Booth, D. Krüerke, G. Heppke, J. Mater. Chem. 1996,
, 927Ϫ934.
6
H
3
1
[9]
1
8
]THF):
), 7.678 (m
6
ortho(para-ph)
δ ϭ 7.804 (s, 1 H, 6-H), 7.695 (m
4
H, H
c
, 2 H, H
c
,
[10]
S. Kumar, S. K. Varshney, Angew. Chem. 2000, 112,
3270Ϫ3272; Angew. Chem. Int. Ed. 2000, 39, 3140Ϫ3142.
[11] [11a]
ortho(meta-ph)
, 4 H, Hortho(ortho-ph)), 7.420 (m
H, H
), 7.647 (m
c
c
, 15
meta
and Hpara) ppm. C NMR, C DEPT, HMQC, HMBC
13
13
B. Kayser, J. Altman, W. Beck, Chem. Eur. J. 1999, 5,
Eur. J. Org. Chem. 2004, 867Ϫ872
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 871

J. Nierle, D. Barth, D. Kuck
FULL PAPER
[
11b]
7
54Ϫ758.
B. Kayser, J. Altman, W. Beck, Tetrahedron 1997,
R. G. Heidenreich, K. Köhler, J. G. E. Krauter, J. Pietsch, Syn-
lett 2002, 1118Ϫ1122, and work quoted therein.
20] [20a]
[
11c]
53, 2475Ϫ2484.
B. Kayser, J. Altman, H. Nöth, J. Knizek,
[
[
W. Beck, Eur. J. Inorg. Chem. 1998, 1791Ϫ1798.
H. A. Dieck, F. R. Heck, J. Organomet. Chem. 1975, 93,
20b]
259Ϫ263. [
R. F. Heck, Acc. Chem. Res. 1979, 12, 146Ϫ151.
A. de Meijere, F. E. Meyer, Angew. Chem. 1994, 106,
2473Ϫ2506; Angew. Chem. Int. Ed. Engl. 1994, 33, 2379.
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[
12] [12a]
R. Boese, A. J. Matzger, D. L. Mohler, K. P. C. Vollhardt,
21]
Angew. Chem. 1995, 107, 1630Ϫ1633; Angew. Chem. Int. Ed.
Engl. 1995, 34, 1478Ϫ1481. [
12b]
K. P. C. Vollhardt, D. L.
[
[
22]
Mohler, in Advances in Strain in Organic Chemistry, (Ed.: B.
Halton), JAI Press, Greenwich, CT,1996; Vol. 5, pp 121Ϫ160.
23] [23a]
1
[22]
Apparently, the H NMR spectrum reported in ref. con-
sisted of a multiplet at δ ϭ 7.34Ϫ7.67 ppm, the magnetic field
[
13] [13a]
A. J. Berresheim, M. Müller, K. Müllen, Chem. Rev. 1999,
strength not being mentioned. [
the combustion analytical data calculated for compounds 1 and
are not distinguishable within the limits of experimental error
see Exp. Sect.).
23b]
It should be noted here that
[
13b]
9
9, 1747Ϫ1785.
S. V. Iyer, M. Wehmeier, J. D. Brand, M.
A. Keegstra, K. Müllen, Angew. Chem. 1997, 109, 1676Ϫ1679;
2
(
Angew. Chem. Int. Ed. Engl. 1997, 36, 1604Ϫ1607. [
13c]
M.
Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen, Angew.
Chem. 1997, 109, 1679Ϫ1682; Angew. Chem. Int. Ed. Engl.
[
24]
25]
For discussions on the electronic absorption spectra of 1 and
[8]
related compounds, see refs.
1
997, 36, 1607Ϫ1610.
[
1
The H NMR spectra of crude and even of singly recrystallized
exhibit a small singlet at δ ϭ 7.76 ppm (i.e., ca. 55 ppb down-
[
[
[
[
14]
F. Diederich, Y. Rubin, Angew. Chem. 1992, 104, 1123Ϫ1146;
Angew. Chem. Int. Ed. Engl. 1992, 31, 1101Ϫ1123.
2
field of the H-6 singlet of 2), which is attributed to the protons
at the central ring of a tetratolane. The EI mass spectra of
some samples exhibit a peak of medium relative intensity at
m/z ϭ 478, indicating the molecular ions of (isomeric) tetratol-
anes.
15] [15a]
U. H. F. Bunz, Synlett 1997, 1117Ϫ1127. [15b] U. H. F.
Bunz, Top. Curr. Chem. 1999, 201, 131Ϫ161.
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M. M. Haley, J. J. Pak, S. C. Brand, Top. Curr. Chem. 1999,
2
01, 81Ϫ130.
[
[
26]
27]
[26a]
For reviews on mass spectrometry of alkylbenzenes, see:
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J. Tellenbröker, D. Kuck, Angew. Chem. 1999, 111,
D. Kuck, Mass Spectrom. Rev. 1990, 9, 181Ϫ233. [
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D. Kuck,
000Ϫ1004; Angew. Chem. Int. Ed. 1999, 38, 919Ϫ922. [
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D.
1
Kuck, A. Schuster, R. A. Krause, J. Tellenbröker, C. P. Exner,
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[27a]
For reviews on the loss of arenes from gaseous ions, see:
[
27b]
D. Kuck, Int. J. Mass Spectrom. 2002, 213, 101Ϫ144.
Kuck, J. Mass Spectrom., in preparation.
D.
3
587Ϫ3613.
[
[
18]
J. Tellenbröker, D. Kuck, Eur. J. Org. Chem. 2001, 1483Ϫ1489.
19] [19a]
[28]
The solubility of hexatolane 1 in organic solvents (including
THF) is very low, much lower than that of pentatolane 2.
Received October 10, 2003
K. Sonogashira, Y. Thoda, N. Hagihara, Tetrahedron Lett.
975, 16, 4467Ϫ4470. [
19b]
For some recent applications, see:
1
872
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 867Ϫ872