The B(C6F5)3 boron Lewis acid route to arene-annulated pentalenes

Article abstract of DOI:10.1002/asia.201400096

4,5-Dimethyl-1,2-bis(1-naphthylethynyl)benzene (12) undergoes a rapid multiple ring-closure reaction upon treatment with the strong boron Lewis acid B(C₆F₅)₃ to yield the multiply annulated, planar conjugated π-system 13 (

Full text of DOI:10.1002/asia.201400096

FULL PAPER
DOI: 10.1002/asia.201400096
The BACHTUNGTRENNUNG(C6F5)3 Boron Lewis Acid Route to Arene-Annulated Pentalenes
Chao Chen,[a] Marcel Harhausen,[a, b] Aiko Fukazawa,[b] Shigehiro Yamaguchi,*[b]
Roland Frçhlich,[a] Constantin G. Daniliuc,[a] Jeffrey L. Petersen,[c] Gerald Kehr,[a] and
Gerhard Erker*[a]
Abstract: 4,5-Dimethyl-1,2-bis(1-naph-
thylethynyl)benzene (12) undergoes
a rapid multiple ring-closure reaction
upon treatment with the strong boron
to yield a mixture of the respective
C6F5- and CH3-substituted dibenzopen-
talenes 10a and 16. The reaction is
thought to proceed through zwitterion-
ic intermediates that exhibit vinyl
(24, 8) with the frustrated Lewis pair
(C6F5)3/P(o-tolyl)3. The overall forma-
tion of the C6F5-substituted products
formally require HB(C6F5)2 cleavage in
an intermediate dehydroboration step.
This was confirmed in the reaction of
B
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Lewis acid B
N
ply annulated, planar conjugated p-
system 13 (50% yield). In the course of
this reaction, a C6F5 group was trans-
ferred from boron to carbon. Treat-
cation reactivities. Some BACHTGNUTERNNU(G C6F5)3-sub-
stituted species (26, 27) consequently
formed by in situ deprotonation upon
treatment of the respective 1,2-bis-
a
thienylethynyl-containing starting
material 21 with B(C6F5)3, which gave
the respective annulated pentalene
product 23 that had the HB(C6F5)2
AHCTUNGTRENNUNG
ment of 12 with CH3B
N
G
ACHTUNGTRENNUNG
ed similarly, giving a mixture of 13
(C6F5-transfer) and the product 15,
which was formed by CH3-group trans-
moiety 1,4-added to its thiophene ring.
Compounds 12–14, 23, and 26 were
characterized by X-ray diffraction.
·
tion · dibenzopentalenes · internal
alkynyl coupling · Lewis acids
fer.
1,2-Bis(phenylethynyl)benzene
(C6F5)2
(8a) reacts similarly with CH3BAHCTUNGTRENNUNG
Introduction
involving typical metal-catalyzed coupling reactions. Here
are a few typical examples: Tilley et al. utilized the Pd-cata-
lyzed coupling of compounds 1a and 2 to produce the di-
Their extended conjugated p-systems at planar polycyclic
frameworks make dibenzopentalenes and their derivatives
very interesting substrates for the development of advanced
organic materials.[1] There are surprisingly few viable syn-
thetic entries to dibenzopentalene systems. Most of them in-
volve metal-induced or metal-catalyzed reactions. Some of
them require quite harsh reaction conditions; some other-
wise very attractive pathways still give rather low yields.[2]
Nevertheless, there has been a small number of attractive di-
benzopentalene syntheses described in the recent literature
phenyl-substituted dibenzopentalene system
3
(and
a number of related derivatives) at high temperature (>
1308C).[3] Kawase et al. found that acetylenic substrates such
as 1b could be homocoupled by treatment with zinc powder
and a nickel catalyst to give the dibenzopentalene deriva-
tives 4 (see Scheme 1).[4] Saito et al. found a unique synthet-
ic entry to dibenzopentalenes by means of treatment of
alkyne 5 with elemental lithium. The dianion of the corre-
sponding dibenzopentalene 4 was probably formed in a radi-
cal pathway. Subsequent oxidation with I2 gave
4
(Scheme 2).[5,6]
[a] Dr. C. Chen,+ Dr. M. Harhausen,+ Dr. R. Frçhlich,++
Dr. C. G. Daniliuc,++ Dr. G. Kehr, Prof. G. Erker
Organisch Chemisches Institut der Universitꢀt Mꢁnster
Corrensstrasse 40, 48149 Mꢁnster (Germany)
E-mail: erker@uni-muenster.de
[b] Dr. M. Harhausen,+ Prof. A. Fukazawa, Prof. S. Yamaguchi
Department of Chemistry Graduate School of Science
Nagoya University
Furo, Chikusa, Nagoya, 464-8602 (Japan)
E-mail: yamaguchi@chem.nagoya-u.ac.jp
[c] Prof. J. L. Petersen++
Bennett Department of Chemistry
West Virginia University
P.O. Box 6045, Morgantown, WV 26506 (USA)
[+] These authors contributed equally to this work.
++] X-ray crystal structure analyses.
[
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201400096.
Scheme 1. Examples of previously reported dibenzopentalene systems.
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Gerhard Erker et al.
indene-type products 11 also involved stoichiometric C6F5-
transfer reactions. These compounds were, however, proba-
bly formed as secondary products from a boron-containing
species during the work-up procedure.[7,8]
We have now substantially extended this reaction and ob-
tained additional mechanistic evidence to understand the
potentially competing pathways taken in the reactions of o-
1,2-bis(arylalkynyl)benzenes with the strongly electrophilic
RB
will be described in this account.
Scheme 2. Redox pathway to a dibenzopentalene derivative.
In a recent communication we disclosed a novel metal-
free entry to dibenzopentalene systems. Our new BACHTUNRGTNEUNG(C6F5)3-
(C6F5)2 reagents.[9,10] These new and extended examples
ACHTUNGTRENNUNG
induced reaction is also special in the sense that it yields un-
symmetrically substituted dibenzopentalenes by a simple
isomerization reaction of o-dialkynylbenzene derivatives
under very mild reaction conditions. The formation of 7
from 6 is an example (see Scheme 3).[7]
Results and Discussion
Reaction of Naphthyl-Substituted Bisalkynylbenzenes
We prepared 1,2-diiodo-4,5-dimethylbenzene from o-xylene
according to a literature procedure.[11] This was then Sono-
gashira coupled[12] with 1-ethynylnaphthalene[13] to give the
bisalkynylbenzene derivative 12 (39%). Compound 12
shows acetylenic 13C NMR resonances of the pair of symme-
try-equivalent CꢀC-naphthyl substituents at d 93.9 and
90.9 ppm, and a respective IR band at n˜ =2172 cmÀ1. Com-
pound 12 was furthermore characterized by X-ray diffrac-
tion. It shows the typical structural features of doubly substi-
tuted alkyne moieties. The conformational arrangement of
the pair of naphthyl substituents at the ends of the linear
alkyne units is close to C2-symmetric (the structure is depict-
ed in the Supporting Information).
Scheme 3. BACHTUNGTRENNUNG(C6F5)3-induced synthesis of 7.
In some cases we observed a more complex reaction path-
way with competing C6F5-transfer. Typical examples are the
reactions of the starting materials 8a,b with B
G
We mixed 12 with BACTHNGUTERN(NUG C6F5)3 (1 molar equiv) at low tem-
gave mixtures of the products 9a,b, 10a,b, and 11a,b
(Scheme 4). The formation of the stoichiometric C6F5-trans-
fer products 10 involved a dehydroboration reaction, which
perature in CH2Cl2 (À208C) and then let the mixture warm
to room temperature, followed by stirring for 2 days. Work-
up involving chromatographic separation eventually gave
the product 13 as a dark red solid in 50% yield and the
minor component 14 (6%) (see Scheme 5). In both cases,
a C6F5 substituent was transferred concurrently with the
ring-closure reactions. Consequently, we have monitored
five 19F NMR resonances of the C6F5 substituent of the
was supported by internal HB
ACHTUGNTREN(NUNG C6F5)2 trapping in a bis-thien-
yl-substituted derivative, and we also observed some B-
ACHTUNGTRENNUNG(C6F5)3-substituted deprotonation products in conjunction
with trapping experiments using bulky amine bases.[7] The
Scheme 4. Preparation of the products 9–11.
Chem. Asian J. 2014, 9, 1671 – 1681
Scheme 5. Formation of the products 13 and 14.
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Gerhard Erker et al.
product 13 at d À138.0/À138.2 (o), À155.2 (p), and À161.39/
À161.44 ppm (m-F of C6F5), indicating a hindered rotation
of the ring (with respect to the NMR time scale). We have
monitored the typical signal of the remaining 1-naphthyl
substituent in 13 and those of the annulated C10H6 unit.
We also reacted the naphthyl-substituted starting material
12 with the methyl group-containing borane CH3B
(C6F5)2.[10]
(C6F5)2-induced 1,1-carbo-
AHCTUNGTRENNUNG
From the chemistry of the alkyl-BACHTNUGTRENNUNG
borations[14,15] we might have expected to find a reaction
route favored by selective methyl-group transfer. However,
1
Compound 13 features H NMR methyl singlets at d 2.14
it turned out that the reaction of CH3BACTHUNGETRN(UNG C6F5)2 with 12 is
(3H) and 1.82 ppm (3H) and the resonances of their adja-
cent CH units at d 6.73 and 5.73 ppm (each 1H), respective-
ly.
rather unselective. We have observed the formation of the
products 13 and 15, formed by C6F5 or CH3 transfer, respec-
tively, in a close to 1:1 molar ratio (Scheme 6). The products
Both the products 13 and 14 were characterized by X-ray
diffraction. The structure of the major product 13 in the
crystal shows the presence of the phenalene framework that
is annulated with the substituted indene building block. The
pentacyclic annulated framework is planar and completely
unsaturated. The indene six-membered ring bears a pair of
methyl substituents and the adjacent five-membered carbo-
cycle bears the C6F5-substituent that had been transferred
from the BACHTUNGTRENNUNG(C6F5)3 Lewis acid during the reaction. It is rotat-
ed almost perpendicular to the indene plane (dihedral angle
C34-C33-C1-C2 À114.6(4)8). The next six-membered ring of
13 has the remaining 1-naphthyl substituent attached to it (q
C14-C13-C23-C32 À98.0(4)8) (see Figure 1).
Scheme 6. Preparation of the products 13 and 15.
were separated by column chromatography. The new prod-
uct 15 was characterized by spectroscopy (CH3: H NMR: d:
1
2.68, 2.22, and 1.81 ppm; for further details, see the Experi-
mental Section and the Supporting Information).
A similar result was obtained when the doubly phenyl-
substituted starting material 8a (see Scheme 4) was reacted
with the boron Lewis acid CH3BACHTUNGRTNEUNG(C6F5)2. Stirring the mixture
for 2 days at room temperature in dichloromethane gave
a mixture of the respective products 10a (formed by C6F5-
transfer) and 16 (formed by transfer of the CH3-group) (see
Scheme 7). The products were separated by chromatogra-
Figure 1. A projection of the molecular structure of compound 13 (ther-
mal ellipsoids are shown with 30% probability). Selected bond lengths
(ꢃ): C1–C2 1.388(4), C2–C14 1.467(4), C14–C15 1.467(4), C15–C20
1.409(4), C2–C3 1.451(4), C3–C12 1.435(4), C12–C11 1.419(4), C11–C13
1.453(4), C13–C14 1.358(4), C3–C4 1.376(4), C4–C5 1.402(4), C5–C6
1.360(5), C6–C7 1.401(5), C7–C12 1.415(5), C15–C16 1.393(4), C16–C17
1.391(4), C17–C18 1.399(5), C18–C19 1.398(4).
Scheme 7. Preparation of the compounds 10a and 16.
phy, and the new product 16 was characterized by spectros-
copy (CH3: d 2.25 (1H), 12.1 ppm (13C), see the Experimen-
tal Section for details).
The minor reaction product 14 shows the NMR resonan-
ces of a pair of different naphthyl substituents. We have
monitored the 1H/13C NMR features of the exocyclic ful-
Variations and Mechanistic Implications
We have shown with a series of examples that 1,2-bis(aryl-
ethynyl)benzenes can readily be converted into substituted
dibenzopentalenes and related systems containing extended
p-systems at planar polycyclic carbon s-frameworks. The
overall boron Lewis acid induced reaction sequences involve
typical carbocation reactivities. This can be formulated for
both the naphthyl- and phenyl-substituted examples. The re-
vene=CHACHTUNGTRENNUNG[naphthyl] unit at d 7.25/134.6 ppm. In addition,
this product also contains a C6F5 substituent at the indene
five-membered carbocycle (19F NMR: d À137.9/À138.0 (o),
À155.6 (p), À162.8/À162.9 ppm (m-F of C6F5). Compound
14 was also characterized by X-ray diffraction (see the Sup-
porting Information for details).
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Gerhard Erker et al.
action sequence followed in the naphthyl series[1a] can prob-
ably be described as follows (see Scheme 8). We assume
that the reaction starts by B(C6F5)3 addition to the proximal
AHCTUNGTRENNUNG
acetylene carbon atom of 12. The ensuing vinyl cation reac-
tivity of a resulting zwitterionic intermediate (17) allows for
the subsequent closure of the five-membered ring to gener-
ate 18, which then might be prone for electrophilic attack
on the adjacent 1-naphthyl substituent (19). C6F5-substituent
migration (20) with subsequent elimination of HBACHTUNRGTNEUNG(C6F5)2
would then directly lead to the observed major product 13.
This general pathway that formally involves a variant of
a 1,1-carboboration at an acetylene carbon atom[1a,15] is sup-
ported by our findings in the corresponding phenyl- and
thienyl-substituted series (see below), where we were able
to deprotonate the B
(o-tolyl)3 as the Lewis base (utilizing the frustrated Lewis
pair effect[16]). We also could trap the HB
(C6F5)2 product
from the necessary dehydroboration reaction in the thienyl
series.
ACHTNUGRTNE(NGNU C6F5)3-substituted intermediate with P-
ACHTUNGTRENNUNG
Scheme 9. a) NEt3, rt, 24 h, [Pd
3 days, [Pd(PPh3)2Cl2] cat., CuI. c) K2CO3, MeOH, rt, 4 h. d) [Pd-
(PPh3)2Cl2] cat., CuI.
ACHTNUGTRNEUN(GN PPh3)2Cl2] cat., CuI. b) NEt3, 608C,
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
We have obtained the supporting evidence for several of
the proposed steps by studying the reactions of a variety of
different substituted 1,2-bis
G
ACHTNUGTNER(NGNU C6F5)3 in pentane at room temperature overnight. Work-up
with B(C6F5)3 under special conditions. Let us first address
G
eventually gave the product 23 as a red-brown solid, isolated
in 40% yield. The X-ray crystal structure analysis (single
crystals were obtained from CH2Cl2/pentane at room tem-
perature by the diffusion method) revealed that the HB-
the retro-hydroboration reaction that we have proposed to
take place at the stage of the reactive intermediate 20 (see
Scheme 8). For that purpose we prepared the unsymmetrical
thienyl-containing bis
means of the synthetic sequence outlined in Scheme 9. Com-
(alkynyl)benzene derivative 21 by
ACHTNUGTNER(UNGN C6F5)2 addition product to a thieno-annulated benzopenta-
lene system[17,18] had been obtained. Product 23 features
pound 21 was then reacted with one molar equivalent of B-
a C6F5 group and a phenyl substituent at the central penta-
lene-derived unit. It shows a BACHTNUTRGNE(UNG C6F5)2 substituent at the
junction with the thiophene framework, whose sulfur atom
forms a dative bond to the adjacent boron Lewis acid [C2-
B1 1.589(3) ꢃ, S1-B1 1.984(2) ꢃ, C2-S1 1.887(2) ꢃ] (see
Figure 2).
Figure 2. Molecular structure of compound 23 (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (ꢃ) and angles (8):
C2–B1 1.589(3), S1–B1 1.984(2), C2–S1 1.887(2), C2–C13 1.505(2), C13–
C14 1.333(3), C14–C15 1.500(3), C2–C3 1.477(2), C3–C4 1.357(3), C3–
C11 1.469(3), C11–C12 1.372(3), C11–C10 1.467(3), C12–C13 1.471(3);
C3-C2-S1 128.5(1), C3-C2-B1 128.8(2), C4-C3-C2 142.7(2).
Scheme 8. Formal mechanistic pathway of the formation of compound
13.
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In solution the internal hydroboration product 23 shows
1H NMR resonances of the CH2 group of the dihydrothio-
phene moiety at d 4.09 and 3.59 ppm (2JHH =17.0 Hz) and of
the adjacent =C-H proton at d 5.43 ppm. Compound 23
shows six separate o-C6F5 19F NMR resonances and three
separate p-C6F5 resonances of the C6F5 substituent at carbon
and both chemically inequivalent C6F5 groups at boron (11B:
À6.9 ppm).
resonance of the [P]H unit at d À13.2 ppm with a typical
1
coupling constant of JPH =482 Hz, and a total of 15 separat-
ed 19F NMR features of the B
ACHTNUGTRNE(UNG C6F5)3 substituent, which con-
tains a chiral propeller conformational geometry that is
“frozen” on the NMR time scale under the applied monitor-
ing conditions at 298 K.
Compound 26 was also characterized by X-ray diffraction
(single crystals were obtained from a layered CH2Cl2/n-hep-
tane mixture at room temperature). The X-ray crystal struc-
ture analysis (see Figure 3) confirmed the regioselective for-
The formation of product 23 indicates that a retro-hydro-
boration is likely to proceed after the C6F5-transfer from
boron to a carbon atom of the pentalene framework had oc-
curred to generate 22 (see Scheme 9; which is the thio-
phene-containing equivalent of intermediate 20 in
Scheme 8). In the case of 22, the liberated HBACHTUNRGTNEUNG(C6F5)2 is then
apparently trapped internally by 1,4-addition to the annulat-
ed thiophene framework at this specific arene/hetarene-an-
nulated pentalene framework.[7]
We have also obtained some experimental support for the
involvement of a dibenzopentalene borate intermediate (see
19, Scheme 8) by using the unsymmetrically substituted bis-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
readily prepared by a twofold Sonogashira coupling reaction
starting from o-bromoiodobenzene (Scheme 10). We then
Figure 3. Molecular structure of the anion of salt 26 (thermal ellipsoids
are shown with 30% probability). Selected bond lengths (ꢃ) and angles
(8): C1–C2 1.482(3), C2–C7 1.424(3), C7–C8 1.482(3), C8–C9 1.371(3),
C9–C10 1.505(3), C10–C15 1.419(3), C15–C16 1.454(3), C16–C1 1.364(3),
C1–C17 1.497(3), C9–B1 1.627(3); C8-C9-B1 133.8(2), C10-C9-B1
120.7(2), C2-C1-C17 125.4(2), C16-C1-C17 128.2(2).
mation of the triply substituted dibenzopentalene frame-
work. Compound 26 shows the methyl group at the terminal
phenylene ring syn-oriented to the n-propyl substituent at
the dibenzopentalene “C-ring” and the bulky BACHTUNRGTNEUNG(C6F5)3 pro-
peller arranged at the opposite sector at the adjacent central
five-membered ring system. The structure features an inde-
pendent [HP
crystal.
(o-tolyl)3]+ phosphonium counter cation in the
ACHTUNGTRENNUNG
Scheme 10. a) NEt3, rt, 24 h, [Pd
ACTHUNGTREN(NUNG PPh3)2Cl2] cat., CuI. b) HNiPr2, 808C,
3 days, [Pd(PPh3)2Cl2] cat., CuI.
ACHTUNGTRENNUNG
We also treated the bis(phenylethynyl)benzene starting
materials 8a and 8b with the B(C6F5)3/P(o-tolyl)3 FLP.
Under similar reaction conditions, this resulted in the forma-
reacted the starting material 24 with the intermolecular frus-
G
ACHTUNGTRENNUNG
[16,19]
trated Lewis pair (FLP) B
at room temperature. Product formation was apparently ini-
tiated by B
A
E
in pentane
tion of the related salts 27a,b in high yield (see Scheme 11).
A
unit, followed by ring closure with the adjacent CꢀC-n-
propyl function and subsequent electrophilic aromatic sub-
stitution to generate the alleged intermediate 25. This was
then effectively deprotonated under the applied reaction
conditions by the bulky PACTHNUTRGNE(UGN o-tolyl)3 Lewis base component of
the FLP to give the observed product 26.
The phosphonium/dibenzopentalenylborate salt 26 was
isolated as a brown solid in 90% yield. In solution it fea-
1
tures the typical H NMR resonances of the n-propyl sub-
stituent, a 11B NMR resonance at d À16.1 ppm, a 31P NMR
Scheme 11. Formation of the salts 27a,b.
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Gerhard Erker et al.
Electronic Structure and Properties of Dibenzopentalenes
and Related p-Electron Systems
The synthesized dibenzopentalenes and related p-electron
systems are an attractive class of molecules with planar
polycyclic skeletons. Kawase and coworkers have already re-
ported that dibenzopentalene derivatives exhibit characteris-
tic absorption spectra with a very weak absorption band in
the long-wavelength region around 600 nm.[3b,4,17] They also
demonstrated that this absorption band is attributable to
forbidden HOMO–LUMO transitions, which are one of the
characteristics of 4np electron systems. We have recently re-
ported the electronic effect of electron-withdrawing C6F5
groups on the electronic structure of dibenzopentalenes,
leading to significant bathochromic shifts of the absorption
bands.[7] With a new phenalene-containing p-conjugated
system in hand, we were interested in the perturbation by
a phenalene moiety in 13 to the electronic structure.
We first evaluated the photophysical properties of the in-
denophenalene p system 13 in comparison with the dibenzo-
pentalene derivative 10b. Figure 4 displays the UV/Vis ab-
sorption spectra of compounds 13 and 10b in acetonitrile.
Figure 5. Energy diagrams and pictorial representations of the HOMO-1,
HOMO, and LUMO of the dibenzopentalene 10b and the relevant phe-
nalene-fused system 13 calculated at the B3LYP/6-31G(d) level, and their
lowest energy transitions estimated by TD-DFT calculations at the
B3LYP/6-31G(d) level.
than 10b. Based on time-dependent DFT (TD-DFT) calcu-
lations, the HOMO–LUMO transition is mainly responsible
for the longest-wavelength absorption in 13. The blue shift
as well as the significantly larger e value in the longest-
wavelength absorption band of 13 compared to 10b is con-
sistent with the results of the calculated values (13: l=
554 nm, f=0.0015; 10b: l=605 nm, f=0.1655).
Another notable feature of the indenophenalene 13 is the
high electrochemical stability as verified by cyclic voltamme-
try (Figure 6). Compound 13 showed reversible redox waves
Figure 4. UV/Vis absorption spectra of 10b (black) and 13 (gray) in ace-
tonitrile.
Compound 13 exhibits the longest-wavelength absorption
band with the maximum wavelength (lmax) of 513 nm with
a relatively large molar extinction coefficient (e=8100),
which contrasts the fact that the longest-wavelength absorp-
tion band of the dibenzopentalene derivative 10b around
600 nm is very weak. This result indicates that the extension
of the p-conjugated skeleton with a phenalene skeleton sig-
nificantly alters the electronic structure and thus the photo-
physical properties.
Figure 6. Cyclic voltammogram of 13 measured in CH2Cl2 (sample: 1 mm;
Bu4N+PF6À: 0.1m; scan rate: 100 mVsÀ1). Fc=ferrocene.
To gain insights into the difference in the electronic struc-
ture between dibenzopentalenes and indenophenalenes,
DFT calculations were conducted for 10b and 13 at the
B3LYP/6-31G(d) level (Figure 5). In 13, both the HOMO
and LUMO are effectively delocalized over the indenophe-
nalene skeleton. Although the character of the LUMOs in
10b and 13 resembles each other, the HOMO and HOMO
À1 in 10b switch the order in 13, presumably due to the ex-
panded p conjugation in the phenalene substructure in the
HOMO of 13. As a result, 13 has a higher-lying HOMO
with first oxidation and reduction potentials of E1/2 =0.68 V
and À1.74 V (versus Fc/Fc+), respectively. These results
demonstrate that the incorporation of the phenalene-fused
structure strongly perturbs the electronic structure, and also
indicate the potential application of this new ring-fused p
skeleton as a building block of redox-active functional or-
ganic dyes.
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Preparation of 4,5-dimethyl-1,2-bis(1-naphthylethynyl)benzene (12)[20]
1,2-Diiodo-4,5-dimethylbenzene (4.2 g, 12 mmol), [Pd(PPh3)Cl2] (750 mg,
Conclusions
AHCTUNGTRENNUNG
Our study shows that rather complex, extended, fully conju-
gated and annulated organic p-systems can rather easily be
obtained by means of sequential carbon–carbon coupling re-
actions initiated and mediated by strongly electrophilic RB-
1.1 mmol), and CuI (400 mg, 2.1 mmol) were dissolved in degassed NEt3
(50 mL). After 1-ethynylnaphthalene (4.0 mL, 35.3 mmol) was added, the
resulting black mixture was heated to 1008C for 12 h. Then all the vola-
tiles were removed in vacuum, and the residue was extracted with diethyl
ether (3ꢄ50 mL). After filtration, diethyl ether was removed in vacuo.
The crude product was washed with a mixture of n-pentane and CH2Cl2
(6:1, 20 mL) and dried to finally give the product as a brown solid (1.9 g,
4.7 mmol, 39%). M.p. 1478C; 1H NMR (500 MHz, CD2Cl2, 298 K): d=
8.54 (d, 3J=8.4 Hz, 1H, 9N-H), 7.88 (d, 3J=8.2 Hz, 1H, 4N-H), 7.86 (d,
3J=8.2 Hz, 1H, 6N-H), 7.81 (d, 3J=7.1 Hz, 1H, 2N-H), 7.55 (s, 1H, 2-H),
7.47 (m, 1H, 3N-H), 7.43 (m, 1H, 7N-H), 7.13 (m, 1H, 8N-H), 2.36 ppm (s,
3H, Me); 13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=138.2 (C-1),
133.59 (C-10N), 133.56 (C-5N), 133.52 (C-2), 131.0 (C-2N), 129.2 (C-4N),
128.5 (C-6N), 127.2 (C-8N), 126.76 (C-7N), 126.75 (C-9N), 125.6 (C-3N),
123.3 (C-3), 121.3 (C-1N), 93.9 (C-4), 90.9 (C-5), 19.8 ppm (Me); IR
(ATR): n˜ =2172 cmÀ1 (CꢀC); HRMS (ESI): m/z calcd for C32H22+Ag+:
513.0767 [M+Ag+]; found: 513.0767.
ACHTUNGTRENNUNG(C6F5)2-type Lewis acids. There are still some selectivity
issues that need attention but we have found promising ex-
amples that indicate a potential usefulness of this method
for forming such extended p-systems easily from readily
available acetylenic precursors.
Experimental Section
General procedures
All syntheses involving air- and moisture-sensitive compounds were car-
ried out using standard Schlenk-type glassware (or in a glove box) under
an atmosphere of argon. Solvents were dried and stored under an argon
atmosphere. NMR spectra were recorded on a Bruker AC 200P, on
a Bruker AV 300, on a Bruker AV 400, on a Varian Inova 500, and on
a Varian UnityPlus 600 spectrometer. 1H NMR and 13C NMR: chemical
shifts d are given relative to TMS and referenced to the solvent signal.
19F NMR: chemical shifts d are given relative to CFCl3 (external refer-
ence, d=0), 11B NMR: chemical shifts d are given relative to BF3·Et2O
(external reference, d=0), 31P NMR: chemical shifts d are given relative
to H3PO4 (85% in H2O) (external reference, d=0). NMR assignments
were supported by additional 2D NMR experiments. Elemental analyses
were performed on an Elementar Vario El III instrument. IR spectra
were recorded on a Varian 3100 FT-IR spectrometer (Excalibur Series).
Melting points were obtained with a DSC Q20 instrument (TA Instru-
ments). Electrospray ionization mass spectra (MS-ESI) were recorded on
a Bruker Micro-TOF machine. Prior exact mass (EM) measurement cali-
bration was performed using sodium formiate clusters. The spectra are
described by listing the calculated mass and the observed signals or by
comparison of the isotopic pattern of the calculated and the measured
X-ray crystal structure analysis of compound 12
Formula C32H22, M=406.50, colorless crystal, 0.28ꢄ0.23ꢄ0.12 mm, a=
8.1726(2), b=11.0699(3), c=13.3109(4) ꢃ, a=101.795(1), b=99.307(1),
g=104.491(2)8, V=1112.14(5) ꢃ3, 1calc =1.214 gcmÀ3, m=0.069 mmÀ1, em-
pirical absorption correction (0.981ꢁTꢁ0.991), Z=2, triclinic, space
ꢀ
group P1 (No. 2), l=0.71073 ꢃ, T=223(2) K, w and f scans, 5568 reflec-
tions collected (Æh, Æk, Æl), [(sinq)/l]=0.59 ꢃÀ1, 3775 independent
(Rint =0.031) and 3184 observed reflections [I>2s(I)], 291 refined param-
eters, R=0.055, wR2 =0.141, max. (min.) residual electron density 0.25
(À0.14) eꢃÀ3, hydrogen atoms calculated and refined as riding atoms.
Preparation of 1-(2-thienylethynyl)-2-(phenylethynyl)benzene (21)
2-Ethynyl-1-(phenylethynyl)benzene (1.11 g, 5.57 mmol, 1 equiv) was dis-
solved in THF (20 mL) and then degassed for 30 min. In another Schlenk
flask o-iodothiophene (1.00 g, 6.01 mmol, 1.1 equiv) was dissolved in
NEt3 (20 mL) and tetrahydrofuran (20 mL), and then degassed. After
30 min, [PdACTHNUGRTNEUNG(PPh3)4] (318 mg, 5 mol%) and CuI (104 mg, 10 mol%) were
added to the Schlenk flask. Subsequently, the diyne solution was trans-
ferred via a canula and the reaction mixture was stirred for 1 day at
608C. Then the reaction mixture was filtered and the filtrate was concen-
trated in vacuo. The obtained residue was first purified by column chro-
matography (n-hexane) and then purified by GPC (CHCl3) yielding com-
pound 21 (1.23 g, 4.32 mmol, 79%) as a yellow brown solid. M.p. 818C;
1H NMR (500 MHz, CD2Cl2, 298 K): d=7.65 (2H), 7.40 (3H)(each m,
signals of the mass.
A preparative gel permeation chromatography
(GPC) system [LC-9201 (Japan Analytical Industry) equipped with
a polystyrene gel column (JAIGEL 1H and 2H, Japan Analytical Indus-
try)] was used for further purification of diyne and pentalene derivatives.
UV/VIS spectra were recorded in Nagoya using a Shimadsu UV-3150
UV-VIS NIR spectrophotometer. Listed are the solvent, the wavelength
of the extinction maxima (lmax), and the molar extinction coefficient e.
X-Ray diffraction: Data sets were collected with a Nonius KappaCCD
diffractometer. Programs used: data collection, COLLECT; data reduc-
tion, Denzo-SMN;[26] absorption correction, Denzo;[27] structure solution,
SHELXS-97;[28] structure refinement, SHELXL-97;[29] and graphics, XP
(BrukerAXS, 2000). Thermals ellipsoids are shown with 30% probability,
R-values are given for observed reflections, and wR2 values are given for
all reflections. Exceptions and special features: Compound 14 crystallized
with one half dichloromethane molecule per asymmetric unit. The struc-
ture was refined with Flack parameter of 0.37(4). CCDC 981779 (12),
CCDC 981780 (13), CCDC 981781 (14), CCDC 981782 (23),
CCDC 981783 (26) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
Ph), 7.59, 7.37 (each m, each 2H, C6H4), 7.37 (2H), 7.07 ppm (1H)ACHTUNGTRENNUNG(m,
C4H3S); 13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=132.6, 128.2, 127.7,
123.4 (C4H3S), 132.1, 131.9, 128.7, 128.5, 125.79, 125.75 (C6H4), 132.0,
129.0, 128.8, 123.4 (Ph), 94.1 (ꢀCPh), 92.3, 88.4 (ꢀC), 87.0 ppm (ꢀC-
A
C20H12S+Na+: 307.0552 [M+Na+]; found: 307.0529.
Preparation of 2-hexynyl-1-(p-tolylethynyl)benzene (24)
1-Bromo-2-(p-tolylethynyl)benzene (1.35 g, 5 mmol, 1 equiv), [Pd-
AHCTUNGTREN(GNUN PPh3)2Cl2] (140 mg, 4 mol%), and CuI (300 mg, 32 mol%) were dis-
solved in degassed HNiPr2 (50 mL). Then 1-pentyne (1 mL, 10 mmol,
2.0 equiv) was added. The resulting black mixture was heated to 808C for
3 days. Subsequently, all volatiles were removed in vacuum, and the ob-
tained residue was extracted with diethylether (3ꢄ50 mL). After filtra-
tion of the ether suspension, the solvent was removed in vacuum, and the
residue was purified by column chromatography (n-pentane). Compound
24 was obtained as an orange-red liquid (644 mg, 2.49 mmol, 50%).
1H NMR (500 MHz, CD2Cl2, 298 K): d=7.56 (m, 1H, 3-H), 7.50 (m, 2H,
o-tol), 7.48 (m, 1H, 6-H), 7.29 (m, 2H, 4,5-H), 7.23 (m, 2H, m-tol), 2.54
(2H), 1.72 (2H), 1.13 (3H)(each m, n-Pr), 2.41 ppm (s, 3H, Me); 13C{1H}
NMR (126 MHz, CD2Cl2, 298 K): d=139.2 (p-tol), 132.3 (C-6), 132.1 (C-
3), 131.9 (o-tol), 129.6 (m-tol), 128.3, 127.7 (C-4,5), 126.9, 126.1 (C-1,2),
120.6 (i-tol), 95.2 (ꢀC-n-Pr), 93.4 ((ꢀCtol), 88.3 ((Cꢀtol), 79.9 (Cꢀn--Pr),
22.7, 22.0, 13.8 (n-Pr), 21.7 ppm (Me); IR (ATR): n˜ =2216 cmÀ1 (CꢀC);
Compounds 8a,[20] 8b,[20] 1,2-diiodo-4,5-dimethylbenzene,[11,20] 1-bromo-2-
(phenylethynyl)benzene,[21,22] 1-bromo-2-(p-tolylethynyl)benzene,[23] 1-
(trimethylsilylethynyl)-2-(phenylethynyl)benzene,[24] and 2-ethynyl-1-
(phenylethynyl)benzene,[22] were prepared according to procedures de-
scribed in the literature.
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Gerhard Erker et al.
HRMS (ESI): m/z calcd for C20H18+Ag+: 365.0454 [M+Ag+]; found:
X-ray crystal structure analysis of compound 14
365.0450.
Single crystals suitable for the X-ray crystal structure analysis were ob-
tained by slow evaporation of a solution of 14 in CH2Cl2. Formula
C38H23F5·0.5 CH2Cl2, M=617.03, colorless crystal, 0.30ꢄ0.05ꢄ0.01 mm,
Reaction of 12 with BACHTUNGTRENNUNG(C6F5)3: Preparation of compounds 13 and 14
BACHTUNGTRENNUNG(C6F5)3 (256 mg, 0.5 mmol, 1 equiv) was dissolved in cold CH2Cl2
a=12.0940(6), b=31.8452(12), c=7.5845(2) ꢃ, V=2921.1(2) ꢃ3, 1calc
=
(À208C, 5 mL) and added to a solution of 4,5-dimethyl-1,2-bis(1-naph-
thylethynyl)benzene (12b) (202 mg, 0.5 mmol, 1 equiv) in cold CH2Cl2
(À208C, 5 mL). The resulting dark red solution was allowed to warm to
room temperature and stirred for 2 days before diethyl ether (grade p.a.,
5 mL) was added. Then all volatiles were removed in vacuo. The ob-
tained residue was purified by column chromatography (cyclohexa-
ne:CH2Cl2 =20:1) to give the products 13 (142 mg, 0.25 mmol, 50%) and
1.403 gcmÀ3, m=1.672 mmÀ1, empirical absorption correction (0.634 ꢁ T
ꢁ 0.983), Z=4, orthorhombic, space group Pnc2 (No. 30), l=1.54178 ꢃ,
T=223(2) K, w and f scans, 12101 reflections collected (Æh, Æk, Æl),
[(sinq)/l]=0.60 ꢃÀ1, 4295 independent (Rint =0.060) and 3354 observed
reflections [I>2s(I)], 413 refined parameters, R=0.052, wR2 =0.135,
max. (min.) residual electron density 0.16 (À0.22) eꢃÀ3, hydrogen atoms
calculated and refined as riding atoms.
14 (18 mg, 0.03 mmol, 6% [ca. 85% pure 1H
ACTHNUGTRNEG(UN CD2Cl2)]) as dark red
solids. Compound 13: M.p. 3118C; 1H NMR (500 MHz, CD2Cl2, 298 K):
d=8.16 (dm, 3J=8.3 Hz, 1H, 4N-H), 8.06 (dm, 3J=8.2 Hz, 1H, 6N-H),
7.90 (dm, 3J=8.1 Hz, 1H, 11-H), 7.87 (dm, 3J=8.0 Hz, 1H, 13-H), 7.77
(dm, 3J=7.8 Hz, 1H, 9-H), 7.75 (dd, 3J=8.3 3J=7.0 Hz, 1H, 3N-H), 7.68
(dm, 3J=8.5 Hz, 1H, 9N-H), 7.64 (dd, 3J=7.0 Hz, J=1.2 Hz, 1H, 2N-H),
Reaction of 12 with MeB
ACHTNUGRTNE(NGNU C6F5)2: Preparation of compounds 13 and 15
MeB(C6F5)2 (183 mg, 0.5 mmol, 1 equiv) was dissolved in cold CH2Cl2
AHCTUNGTRENNUNG
(À208C, 5 mL) and added to a solution of diyne 12 (202 mg, 0.5 mmol,
1 equiv) in cold CH2Cl2 (À208C, 5 mL). The dark red reaction solution
was then allowed to warm to room temperature and stirred for 2 days
before diethyl ether (p.a., 5 mL) was added. Subsequently, all volatiles
were removed in vacuo. The obtained residue was purified by column
chromatography (cyclohexane:CH2Cl2 =20:1) to give the products 13
(48 mg, 0.08 mmol, 17%) and 15 (58 mg, 0.10 mmol, 20%), each as
3
7.53 (m, 1H, 10-H), 7.53 (m, 1H, 7N-H), 7.36 (dd, J=8.0 Hz, 7.4 Hz, 1H,
14-H), 7.31 (m, 1H, 8N-H), 7.18 (dd, 3J=7.4 Hz, 4J=1.1 Hz, 1H, 15-H),
6.73 (s, 1H, 4-H), 5.73 (s, 1H, 1-H), 2.14 (s, 3H, 3-Me), 1.82 ppm (s, 3H,
2-Me); 13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=141.3, 137.5 (C-
5,18), 139.5 (C-17), 137.0 (C-3), 135.4 (C-1N), 134.2 (C-5N), 134.1 (C-2),
133.6 (C-12), 133.0 (C-16), 132.9 (C-7), 132.7 (C-10N), 131.21 (C-13),
131.15 (C-19), 130.0 (C-15), 129.5 (C-11), 129.1 (C-4N), 128.9 (C-8), 128.7
(C-6N), 127.9 (C-2N), 127.4, 126.7 (C-10,7N), 127.0 (C-14), 126.9 (C-8N),
126.3 (C-3N), 126.2 (C-20), 126.1 (C-9N), 125.4 (C-1), 125.2 (C-9), 120.6
(C-4), 119.2 (br, C-6), 20.24 (2-Me), 20.20 ppm (3-Me), [C6F5 not listed];
19F NMR (470 MHz, CD2Cl2, 298 K): d=À138.0, À138.2 (each m, each
1F, o-C6F5), À155.2 (t, 3J=20.7 Hz, 1F, p-C6F5), À161.39, À161.44 ppm
(each m, each 1F, m-C6F5), [Dd19Fmp =6.2]; UV/Vis (CH3CN): lmax (log
e)=350 nm (4.04), 439 nm (4.09), 513 nm (3.91); HRMS (ESI): m/z calcd
for [C38H21F5+Na+]: 595.1456 [M+Na+]; found: 595.1457.
a
dark red solid. Compound 15: M.p. 2128C; 1H NMR (500 MHz,
3 3
CD2Cl2, 298 K): d=8.27 (d, J=7.8 Hz, 1H, 9-H), 8.12 (d, J=8.3 Hz, 4N-
H), 8.03 (d, 3J=8.2 Hz, 1H, 6N-H), 7.83 (d, 3J=7.8 Hz, 1H, 11-H), 7.79
(d, 3J=8.0 Hz, 1H, 13-H), 7.73 (t, 3J=7.8 Hz, 1H, 10-H), 7.72 (dd, 3J=
8.3 Hz, 6.9 Hz, 1H, 3N-H), 7.63 (d, 3J=8.6 Hz, 1H, 9N-H), 7.58 (dd, 3J=
6.9 Hz, 4J=1.1 Hz, 1H, 2N-H), 7.50 (ddd, 3J=8.2 Hz, 6.7 Hz, 4J=1.0 Hz,
1H, 7N-H), 7.30 (dd, 3J=8.0, 7.3 Hz, 1H, 14-H), 7.26 (ddd, 3J=8.6 Hz,
6.7 Hz, J=1.1 Hz, 1H, 8N-H), 7.20 (s, 1H, 4-H), 7.02 (d, 3J=7.3 Hz, 1H,
4
15-H), 5.64 (s, 1H,1-H), 2.68 (s, 3H, 6-Me), 2.22 (s, 3H, 3-Me), 1.81 ppm
(s, 3H, 2-Me); 13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=143.7 (C-5),
138.4 (C-18), 136.4 (C-3), 136.2 (C-1N), 135.4 (C-17), 134.9 (C-6), 134.3
(C-5N), 134.0 (C-16), 133.8 (C-12), 133.4 (C-2), 132.9 (C-10N), 131.9 (C-
19), 131.1 (C-8), 129.5 (C-13), 128.71 (C-7), 128.68 (C-4N), 128.63 (C-6N),
128.0 (C-2N), 127.5 (C-15), 127.3 (C-10), 127.0 (C-11), 126.9 (C-20), 126.7
(C-8N), 126.6 (C-14), 126.5 (C-7N), 126.3 (C-3N), 126.1 (C-9N), 125.4 (C-9),
125.0 (C-1), 120.6 (C-4), 20.3 (3-Me), 20.2 (2-Me), 14.1 ppm (6-Me); UV/
Vis (CH3CN): lmax (log e)=342 nm (4.11), 417 nm (3.94), 510 nm (3.74);
HRMS (ESI): m/z calcd for [C33H24+Na+]: 443.1770 [M+Na+]; found:
443.1770.
X-ray crystal structure analysis of compound 13
Single crystals suitable for the X-ray crystal structure analysis were ob-
tained by slow evaporation of a solution of 13 in CH2Cl2. Formula
C38H21F5, M=572.55, red crystal, 0.20ꢄ0.17ꢄ0.03 mm, a=30.7143(10),
b=7.4972(2), c=24.9464(8) ꢃ, b=110.193(2)8, V=5391.4(3) ꢃ3, 1calc=
1.411 gcm-3, m=0.878 mm-1, empirical absorption correction (0.843ꢁTꢁ
0.974), Z=8, monoclinic, space group C2/c (No. 15), l=1.54178 ꢃ, T=
223(2) K, w and f scans, 22682 reflections collected (Æh, Æk, Æl),
[(sinq)/l]=0.60 ꢃ-1, 4541 independent (Rint =0.064) and 3141 observed
reflections [I>2s(I)], 390 refined parameters, R=0.061, wR2=0.157,
max. (min.) residual electron density 0.18 (À0.26) eꢃÀ3, hydrogen atoms
calculated and refined as riding atoms.
Reaction of 1,2-bis(phenylethynyl)benzene (8a) with MeB
Preparation of compounds 10a[7,20] and 16
ACHTNUGTERN(NGNU C6F5)2:
MeB
ACHTUNGTRENNUNG
(À208C, 5 mL) and added to
a
1
Compound 14: M.p. 2108C; H NMR (500 MHz, CD2Cl2, 299 K): d=8.01
1.0 mmol, 1 equiv) in cold CH2Cl2 (À208C, 5 mL). The resulting dark red
solution was allowed to warm to room temperature and then stirred for 2
days before diethyl ether (p.a., 5 mL) was added. Subsequently, all vola-
tiles were removed in vacuo, and the obtained residue was purified by
column chromatography (cyclohexane:dichloromethane=20:1) to give
the products 16 (71 mg, 0.24 mmol, 24%) and 10a (65 mg, 0.15 mmol,
15%), each as a yellow solid. Compound 16: M.p. 1468C.; 1H NMR
(500 MHz, CD2Cl2, 298 K): d=7.64 (m, 2H, o-Ph), 7.51 (m, 2H, m-Ph),
7.44 (m, 1H, p-Ph), 7.26 (dm, J=7.4 Hz, 1H, 9-H), 7.12 (dm, J=7.4 Hz,
1H, 1-H), 7.05 (dm, 3J=7.4 Hz, 1H, 12-H), 6.98 (m, 1H, 10-H), 6.93 (m,
3H, 3,4,11-H), 6.82 (m, 1H, 2-H), 2.25 ppm (s, 3H, Me); 13C{1H} NMR
(126 MHz, CD2Cl2, 298 K): d=151.6 (C-5), 149.6 (C-13), 143.4 (C-7),
143.3 (C-15), 139.1 (C-14), 138.9 (C-6), 135.9 (C-8), 135.3 (C-16), 134.3 (i-
Ph), 128.99 (m-Ph), 128.96 (p-Ph), 128.9 (o-Ph), 128.3 (C-3), 127.7 (C-2),
127.45, 127.42 (C-10,11), 122.6 (C-12), 122.4 (C-9), 121.7 (C-1), 121.2 (C-
4), 12.1 ppm (Me); UV/Vis (CH3CN): lmax (log e)=406 nm (3.88),
514 nm (1.80); HRMS (ESI): m/z calcd for C23H16+Ag+: 399.0298
[M+Ag+]; found: 399.0298.
(m, 1H, 19N-H), 7.92 (dm, 3J=8.5 Hz, 1H, 4N-H), 7.91 (dm, 3J=8.6 Hz,
1H, 6N-H), 7.89 (m, 1H, 16N-H), 7.88 (m, 1H, 14N-H), 7.79 (dm, 3J=
7.1 Hz, 1H, 2N-H), 7.73 (dm, 3J=8.1 Hz, 1H, 9N-H), 7.54 (m, 1H, 3N-H),
7.53 (m, 1H, 12N-H), 7.51 (m, 1H, 13N-H), 7.50 (m, 3H, 7N,17N,18N-H),
7.41 (ddd, 3J=8.1, 6.9 Hz, 4J=1.4 Hz, 1H, 8N-H), 7.25 (s, 1H, 9-H), 7.04
(s, 1H, 1-H), 6.82 (s, 1H, 4-H), 2.23 (s, 3H, 3-Me), 2.03 ppm (s, 3H, 2-
Me); 13C{1H} NMR (126 MHz, CD2Cl2, 299 K): d=143.8 (C-7), 143.1 (C-
8), 140.9 (C-5), 137.5 (C-3), 134.7 (C-2), 134.6 (C-9), 134.1, 133.98,
133.96, 132.1 (C-1N,5N,11N,15N), 133.3 (C-20N), 132.2 (C-10), 131.8 (C-10N),
129.4 (C-4N), 128.9 (C-14N), 128.81 (C-6N), 128.77 (d, J=1.1 Hz, C-12N),
128.5 (C-16N), 128.1 (m, C-6), 127.7 (C-2N), 126.72 (C-8N), 126.68 (d, J=
1.5 Hz, C-19N), 126.6 (C-7N), 126.5 (C-18N), 126.3 (C-17N), 125.6 (C-3N),
3
3
125.5 (C-13N), 125.2 (C-9N), 125.2 (C-1), 120.9 (C-4), 20.23 (3-Me),
t
20.15 ppm (2-Me). [n.o. (C6F5);
tentatively assigned]; 19F NMR
(470 MHz, CD2Cl2, 299 K): d=À137.9, À138.0 (each m, each 1F, o-C6F5),
À155.6 (t, 3J=20.9 Hz, 1F, p-C6F5), À162.8, À162.9 ppm (each m, each
1F, m-C6F5), [Dd19Fmp =7.2, 7.3]; HRMS (ESI): m/z calcd for
[C38H23F5+Na+]: 597.1612 [M+Na+]; found: 597.1618.
Preparation of compound 23
The diyne 21 (60.0 mg, 211 mmol, 1 equiv) was mixed with dry n-pentane
(5 mL). Then BACHTNUTRGNE(UNG C6F5)3 (108 mg, 211 mmol, 1 equiv) dissolved in dry n-
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Gerhard Erker et al.
pentane (5 mL) was added at room temperature. The reaction mixture
turned dark red-brown immediately, and the obtained suspension was
stirred overnight. Then the supernatant was removed with a pipette, and
the solid residue was washed with n-pentane (3ꢄ2 mL). After drying in
vacuo, the product was isolated as a brown solid (67.2 mg, 84.3 mmol,
40%). Decomp. 1478C; 1H NMR (600 MHz, CD2Cl2, 298 K): d=7.86
(dm, 3J=7.6 Hz, 1H, 1-H), 7.77 (m, 2H, o-Ph), 7.60 (m, 2H, m-Ph), 7.56
(m, 1H, p-Ph), 7.31 (td, 3J=7.6 Hz, 4J=1.1 Hz, 1H, 3-H), 7.18 (td, 3J=
7.6 Hz, 4J=1.1 Hz, 1H, 2-H), 6.94 (ddm, 3J=7.6 Hz, JFH =4.1 Hz, 1H, 4-
H), 5.43 (dd, 3J=3.8 Hz, 2.3 Hz, 1H, 11-H), 4.09 (dd, 2J=17.0 Hz, 3J=
3.8 Hz, 1H, 10-Ha), 3.59 (dd, 2J=17.0 Hz, 3J=2.3 Hz, 1H, 10-Hb);
13C{1H} NMR (151 MHz, CD2Cl2, 298 K): d=160.1 (m, C-12), 149.7 (C-
14), 147.0 (C-5), 146.4 (C-7), 143.0 (d, J=1.8 Hz, C-13), 133.1 (i-Ph),
130.49 (p-Ph), 130.45 (C-15), 129.7 (C-3), 129.4 (m-Ph), 129.3 (o-Ph),
125.7 (C-2), 124.1 (C-1), 120.7 (d, J=3.5 Hz, C-4), 113.5 (br, C-6), 111.5
(C-11), 75.7 (br, C-8), 46.5 ppm (C-10), [C6F5 not listed]; 11B{1H} NMR
(192 MHz, CD2Cl2, 298 K): d=À6.9 ppm (n1/2 ~300 Hz); 19F NMR
(564 MHz, CD2Cl2, 298 K): d=À129.1 (m, o), À132.8 (m, o’), À154.5 (t,
(o’), À163.8 (t, 3JFF =20.4 Hz, p), À166.0 (m), À166.9 ppm (m’) (each m,
each 1F, BC6F5), [Dd19Fpm =2.2, 3.1]. 31P NMR (243 MHz, 298 K,
1
CD2Cl2): d=À13.2 ppm (dm, JPH ꢂ482 Hz); HRMS (ESI): m/z calcd for
(C21H21P)2+Ag+: 717.1807 [M2+Ag+]; found: 717.1809; m/z calcd for
C38H17BF15À: 769.1184 [MÀ]; found: 769.1218.
X-ray analysis of compound 26
Crystals suitable for X-ray crystal structure analysis were obtained by the
diffusion method of a layered CH2Cl2/n-heptane solution at room temper-
ature. Formula C59H39BF15P, M =1074.68, orange crystal, 0.40ꢄ0.20ꢄ
0.15 mm, a=12.6060(3), b=20.7988(3), c=19.4554(6) ꢃ, b=104.734(2)8,
V=4933.3(2) ꢃ3, 1calc =1.447 gcmÀ3, m=1.356 mmÀ1, empirical absorption
correction (0.613ꢁTꢁ0.822), Z=4, monoclinic, space group P21/n (No.
14), l=1.54178 ꢃ, T=223(2) K, w and f scans, 48272 reflections collect-
ed (Æh, Æk, Æl), [(sinq)/l]=0.60 ꢃÀ1, 8606 independent (Rint =0.043)
and 7850 observed reflections [I>2s(I)], 693 refined parameters, R=
0.047, wR2 =0.125, max. (min.) residual electron density 1.06 (À0.45)
eꢃÀ3, hydrogen atoms calculated and refined as riding atoms.
3JFF =20.0 Hz, p), À162.1 (m, m’), À162.6 (m, m) (each 1F, BC6F5),
3
[Dd19Fpm =7.6, 8.1]; À130.8, À132.1 (each br m, o), À155.5 (t, JFF
=
=
Preparation of compound 27a
19.9 Hz, p), À162.57, À162.62 (each m, m’) (each 1F, BC6F5), [Dd19Fpm
7.1]; À135.0, À136.3 (each m, o), À154.9 (t, 3JFF =20.4 Hz, p), À161.5,
À162.8 ppm (each m, m) (each 1F, C6F5), [Dd19Fpm =6.6, 7.9]; HRMS
(ESI): m/z calcd for C38H12BF15SÀH+: 795.0447 [MÀH]; found: 795.0448.
Compound 8a[20] (25.0 mg, 89.8 mmol, 1 equiv) and tri
(27.3 mg, 89.8 mmol, 1 equiv) were dissolved in dry n-pentane (5 mL).
Then a solution of B(C6F5)3 (46.0 mg, 89.8 mmol, 1 equiv) in dry n-pen-
ACHTUNGTREN(NUNG o-tolyl)phosphane
AHCTUNGTRENNUNG
tane (5 mL) was added at room temperature. The mixture turned dark
red-brown immediately. The obtained suspension was stirred overnight.
Subsequently, the supernatant was removed with a pipette, and the solid
residue was washed with n-pentane (3ꢄ2 mL). After drying in vacuo, the
product was obtained as a brown solid (95 mg, 86.8 mmol, 97%). M.p.
1168C; 1H NMR (500 MHz, CD2Cl2, 298 K): d=pentalene anion: 7.50
(m, 2H, o-Ph), 7.42 (m, 2H, m-Ph), 7.37 (m, 1H, p-Ph), 7.00 (dm, 3J=
7.5 Hz, 1H, 4-H), 6.94 (dm, 3J=7.5 Hz, 1H, 1-H), 6.85 (dm, 3J=7.5 Hz,
1H, 12-H), 6.72 (td, 3J=7.5 Hz, 4J=1.1 Hz, 1H, 11-H), 6.66 (td, 3J=
X-ray crystal structure analysis of compound 23
Crystals suitable for the X-ray crystal structure analysis were obtained by
diffusion method of a layered CH2Cl2/n-heptane solution at room temper-
ature. Formula C38H12BF15S, M =796.35, orange crystal, 0.37ꢄ0.15ꢄ
0.10 mm, a=16.9719(7), b=8.8408(3), c=21.3311(5) ꢃ, b=102.748(2)8,
V=3121.73(18) ꢃ3, 1calc =1.694 gcmÀ3, m=2.038 mmÀ1, empirical absorp-
tion correction (0.519ꢁTꢁ0.822), Z=4, monoclinic, space group P21/
c (No. 14), l=1.54178 ꢃ, T=223(2) K, w and f scans, 26907 reflections
4
3
4
collected (Æh, Æk, Æl), [(sinq)/l]=0.60 ꢃÀ1, 5423 independent (Rint
=
7.5 Hz, J=1.3 Hz, 1H, 3-H), 6.58 (td, J=7.5 Hz, J=1.2 Hz, 1H, 10-H),
6.57 (td, 3J=7.5 Hz, 4J=1.1 Hz, 1H, 2-H), 5.63 (dd, 3J=7.5 Hz, JFH
4.5 Hz, 1H, 9-H). [HP
(o-tol)3] cation: 8.31 (br d, 1JPH =483.3 Hz, 1H,
=
0.041) and 4904 observed reflections [I>2s(I)], 497 refined parameters,
R=0.036, wR2 =0.112, max. (min.) residual electron density 0.22 (À0.21)
eꢃÀ3, hydrogen atoms calculated and refined as riding atoms.
AHCTUNGTRENNUNG
PH), 7.74 (m, 3H, p-otol), 7.52 (m, 3H, m’-otol), 7.40 (m, 3H, m-otol),
7.10 (dd, 3JPH =16.0 Hz, 3J=7.8 Hz, 3H, o-otol), 2.32 ppm (s, 9H, Me);
13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=pentalene anion: 160.4 (br,
C-6), 157.8 (d, JFC =4.4 Hz, C-5), 150.2 (C-13), 147.0 (C-7), 146.5 (C-15),
138.4 (C-8), 135.35 (C-14), 135.32 (C-16), 135.1 (i-Ph), 129.2 (o-Ph),
128.69 (m-Ph), 128.1 (p-Ph), 127.8 (C-3), 126.1 (C-10), 125.6 (C-11), 125.5
Preparation of compound 26
The diyne 24 (50.0 mg, 194 mmol, 1 equiv) and tri
(59.1 mg, 194 mmol, 1 equiv) were dissolved in dry n-pentane (5 mL).
Then a solution of B(C6F5)3 (99.6 mg, 194 mmol, 1 equiv) in dry n-pentane
ACHTUNGTREN(NUNG o-tolyl)phosphane
ACHTUNGTRENNUNG
(C-2), 124.5 (d, JFC =6.4 Hz, C-9), 123.7 (d, JFC =7.7 Hz, C-4), 121.1 (C-
(5 mL) was added at room temperature. The reaction mixture turned
dark red-brown immediately. The obtained suspension was stirred over-
night. Subsequently, the supernatant was removed with a pipette, and the
solid residue was washed with n-pentane (3ꢄ2 mL). After drying in
vacuo, the product was isolated as a brown solid (188 mg, 175 mmol,
90%). M.p. 2138C; 1H NMR (600 MHz, CD2Cl2, 298 K): d=pentalene
anion: 7.00 (dm, 3J=7.4 Hz, 1H, 1-H), 6.92 (dm, 3J=7.4 Hz, 1H, 4-H),
2
12), 120.3 (C-1), [C6F5 not listed]. [HP
G
=
9.0 Hz, o’-otol), 136.9 (d, 4JPC =2.8 Hz, p-otol), 134.9 (d, 2JPC =12.8 Hz,
o-otol), 133.4 (d, JPC =10.7 Hz, m’-otol), 128.67 (d, JPC =13.8 Hz, m-otol),
3
111.9 (d, 1JPC =87.8 Hz, i-otol), 21.0 ppm (d, 3JPC =8.6 Hz, Me); 11B{1H}
NMR (160 MHz, CD2Cl2, 298 K): d=À16.0 ppm (n1/2 ꢂ50 Hz). 19F NMR
3
(470 MHz, CD2Cl2, 298 K): d=À127.0 (o), À129.6 (o’), À163.4 (t, JFF
=
20.6 Hz, p), À166.5 (m), À167.8 (m’) (each m, each 1F, BC6F5),
[Dd19Fpm =3.1, 4.4]; À127.1 (o), À132.7 (o’), À163.5 (t, 3JFF =20.4 Hz, p),
À166.7 (m’), À167.1 (m) (each m, each 1F, BC6F5), [Dd19Fpm =3.2, 3.6];
À127.8 (o), À133.5 (o’), À163.3 (t, 3JFF =20.3 Hz, p), À165.6 (m’),
À166.6 ppm (m) (each m, each 1F, BC6F5), [Dd19Fpm =2.3, 3.3]; 31P NMR
3
3
6.68 (tm, J=7.4, 7.4 Hz, 1H, 2-H), 6.64 (m, 1H, 12-H), 6.63 (tm, J=7.4,
7.4 Hz, 1H, 3-H), 6.33 (d, 3J=7.7 Hz, 1H, 10-H), 5.36 (dd, 3J=7.7 Hz,
J
FH =4.5 Hz, 1H, 9-H), 2.51 (m, 2H, 14-CH2), 2.15 (s, 3H, 11-Me), 1.61
3
(m, 2H, CH2), 1.00 (t, J=7.4 Hz, 3H, CH3). [HPACTHNUTRGNE(NUG o-tol)3] cation: 8.37 (d,
1JPH =482.5 Hz, 1H, PH), 7.79 (m, 3H, p-otol), 7.57 (m, 3H, m’-otol), 7.45
(m, 3H, m-otol), 7.14 (dd, 3JPH =16.0 Hz, 3J=7.9 Hz, 3H, o-otol),
2.38 ppm (s, 9H, Me); 13C{1H} NMR (151 MHz, CD2Cl2, 298 K): d=pen-
talene anion: 157.8 (m, C-5), 151.5 (C-13), 146.9 (C-7), 146.5 (C-15),
136.98 (C-14), 136.0 (C-16), 135.9 (C-8), 135.2 (C-11), 126.8 (C-3), 126.2
(C-10), 124.9 (C-2), 123.8 (d, J=6.1 Hz, C-9), 123.2 (dm, J=8.1 Hz, C-4),
(202 MHz, CD2Cl2, 298 K): d=À13.0 ppm (br d, JPH ꢂ 483 Hz); elemen-
tal analysis calcd (%) for C61H35BF15P: C 66.93, H 3.22; found: C 67.21,
H 3.18.
Preparation of compound 27b
121.0 (C-12), 120.5 (C-1), 28.5 (14-CH2), 22.6 (CH2), 21.3 (11-Me), 14.7
Compound 8b[20] (25.0 mg, 81.3 mmol, 1 equiv) and tri
(24.7 mg, 81.3 mmol, 1 equiv) were dissolved in dry n-pentane (5 mL).
Then a solution of B(C6F5)3 (41.7 mg, 81.3 mmol, 1 equiv) in dry n-pen-
ACHTUNGTREN(NUNG o-tolyl)phosphane
2
(CH3), n.o. (C-6), [C6F5 not listed]. [HP
(o-tol)3] cation: 143.8 (d, JPC
=
9.0 Hz, o’-otol), 137.00 (p-otol), 135.0 (d, 2JPC =12.8 Hz, o-otol), 133.5 (d,
ACHTUNGTRENNUNG
3JPC =10.8 Hz, m’-otol), 128.8 (d, 3JPC =13.9 Hz, m-otol), 111.9 (d, JPC
=
tane (5 mL) was added at room temperature. The reaction mixture
turned dark red-brown immediately. After stirring the suspension over-
night, the supernatant was removed with a pipette, and the solid residue
was washed with n-pentane (3ꢄ2 mL). After drying in vacuo, the product
was obtained as a brown solid (85 mg, 75.7 mmol, 93%). M.p. 1248C.
1H NMR (500 MHz, CD2Cl2, 298 K): d=pentalene anion: 7.52 (m, 2H,
o-Ph),7.42 (m, 2H, m-Ph), 7.35 (m, 1H, p-Ph), 6.83 (dm, 3J=7.5 Hz, 1H,
1
87.8 Hz, i-otol), 21.1 ppm (d, 3JPC =8.6 Hz, Me); 11B{1H} NMR (192 MHz,
298 K, CD2Cl2): d=À16.1 ppm (n1/2 ꢂ50 Hz); 19F NMR (564 MHz,
CD2Cl2, 298 K): d=À127.2 (o), À129.8 (o’), À163.9 (t, 3JFF =20.4 Hz, p),
À166.7 (m’), À168.1 (m) (each m, each 1F, BC6F5), [Dd19Fpm =2.8, 4.2];
À127.3 (o), À133.0 (o’), À164.1 (t, 3JFF =20.5 Hz, p), À167.1 (m), À167.3
(m’) (each m, each 1F, BC6F5), [Dd19Fpm =3.0, 3.2]; À127.8 (o), À133.6
Chem. Asian J. 2014, 9, 1671 – 1681
1679
ꢂ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Gerhard Erker et al.
12-H), 6.77 (s, 1H, 4-H), 6.73 (s, 1H, 1-H), 6.69 (td, 3J=7.5 Hz, 4J=
1.0 Hz, 1H, 11-H), 6.53 (td, 3J=7.5 Hz, 4J=1.0 Hz, 1H, 10-H), 5.58 (dd,
g) M. D. Watson, A. Fechtenkçtter, K. Mꢁllen, Chem. Rev. 2001,
101, 1267–1300; h) M. Bendikov, F. Wudl, D. F. Perepichka, Chem.
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5028–5048; j) S. Sergeyev, W. Pisula, Y. H. Geerts, Chem. Soc. Rev.
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Ed. 2010, 49, 9068–9093.
3J=7.5 Hz, JFH =4.5 Hz, 1H, 9-H), 1.94 (s, 6H, 2,3-Me). [HP
A
cation: 8.33 (br d, JPH =482.3 Hz, 1H, PH), 7.76 (m, 3H, p-otol), 7.54 (m,
3H, m’-otol), 7.42 (m, 3H, m-otol), 7.11 (dd, 3JPH =16.0 Hz, 3J=7.8 Hz,
3H, o-otol), 2.33 ppm (s, 9H, Me); 13C{1H} NMR (126 MHz, CD2Cl2,
298 K): d=pentalene anion: 160.7 (br, C-6), 155.9 (d, JFC =4.7 Hz, C-5),
150.2 (C-13), 146.9 (C-15), 146.5 (C-7), 138.4 (C-8), 135.6 (C-3),135.4 (i-
Ph), 134.0 (C-14), 133.2 (C-2), 133.1 (C-16), 129.2 (o-Ph), 128.6 (m-Ph),
127.9 (p-Ph), 125.8 (C-10), 125.4 (dm, JFC =8.1 Hz, C-4),125.3 (C-11),
124.2 (d, JFC =6.3 Hz, C-9), 121.9 (C-1), 120.8 (C-12), 20.1 (3-Me), 19.7
1
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(2-Me), [C6F5 not listed]. [HPACHTUNGTRNEUNG
(o-tol)3] cation: 143.8 (d, 2JPC =9.1 Hz,
o’-otol), 136.9 (br, p-otol), 134.9 (br d, 2JPC =12.8 Hz, o-otol), 133.4 (br d,
3JPC =10.7 Hz, m’-otol), 128.7 (br d, 3JPC =13.5 Hz, m-otol), 111.9 (br d,
1JPC =88.1 Hz, i-otol), 21.0 ppm (d, 3JPC =8.9 Hz, Me); 11B{1H} NMR
(160 MHz, CD2Cl2, 298 K): d=À16.1 (n1/2 ꢂ50 Hz). 19F NMR (470 MHz,
CD2Cl2, 298 K): d=À126.9 (o), À129.8 (o’), À163.5 (t, 3JFF =20.2 Hz, p),
À166.7 (m), À167.9 (m’) (each m, each 1F, BC6F5), [Dd19Fpm =3.2, 4.4];
À127.2 (o), À132.5 (o’), À163.7 (t, 3JFF =20.8 Hz, p), À166.9 (m’), À167.2
(m) (each m, each 1F, BC6F5), [Dd19Fpm =3.2, 3.5]; À127.8 (o), À133.5
(o’), À163.4 (t, 3JFF =20.2 Hz, p), À165.7 (m’), À166.7 ppm (m) (each m,
each 1F, BC6F5), [Dd19Fpm =2.3, 3.3]; 31P NMR (202 MHz, CD2Cl2,
1
298 K): d=À13.0 ppm (br d, JPH ꢂ482 Hz); elemental analysis calcd (%)
for C63H39BF15P: C 67.40, H 3.50; found: C 67.02, H 3.34.
Photophysical properties
UV/VIS spectra were recorded using a Shimadzu UV-3150 UV-VIS-NIR
spectrophotometer with a resolution of 0.5 nm. Dilute solutions in spec-
tral grade solvents in a 1 cm square quartz cuvette were used for the
measurements.
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Electrochemical properties
Cyclic voltammograms were recorded on an ALS/CHI-617A electro-
chemical analyzer (BAS). The CV cell consisted of a glassy carbon elec-
trode, a Pt counter electrode, and an Ag/AgNO3 reference electrode. The
measurements were carried out under an argon atmosphere using CH2Cl2
solutions of samples with a concentration of 1 mm and 0.1m tetrabutylam-
monium hexafluorophosphate as a supporting electrolyte. Redox poten-
tials were calibrated with the ferrocene/ferrocenium couple as an internal
standard.
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Computational method
Geometry optimization of a series of dibenzopentalene derivatives were
performed with the B3LYP theory and 6-31G(d) basis set, implemented
in the Gaussian 09 Program.[25] All stationary points were optimized with-
out any symmetry assumptions and characterized by normal coordinate
analysis at the same level of theory (the number of imaginary frequen-
cies, NIMAG, was 0). Time-dependent density functional theory (TD-
DFT) vertical excitation calculations were performed using the B3LYP
theory and 6-31G(d) basis set as implemented in the Gaussian 09 pro-
gram.
Acknowledgements
Financial support from the Deutsche Forschungsgemeinschaft is grateful-
ly acknowledged.
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Received: January 20, 2014
Revised: February 13, 2014
Published online: March 28, 2014
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