Synthesis of a 2D lander

Article abstract of DOI:10.1002/ejoc.200600675

A method for the preparation of an asymmetric superbenzene is presented. The synthesis proceeds through the 12-fold cyclodehydrogenation of a polyaromatic precursor obtained by successive Diels-Alder additions of cyclopentadienones and alkynes. Wiley-VCH

Full text of DOI:10.1002/ejoc.200600675

FULL PAPER
DOI: 10.1002/ejoc.200600675
Synthesis of a 2D Lander
Chaitali Basu,[a,b] Cecile Barthes,[a] Subir K. Sadhukhan,[a,c] Navdeep K. Girdhar,[a,d] and
André Gourdon*[a]
Keywords: Molecular devices / Nanotechnology / Arenes / Cycloadditions / Diels–Alder reactions
A method for the preparation of an asymmetric superben-
zene is presented. The synthesis proceeds through the 12-
fold cyclodehydrogenation of a polyaromatic precursor ob-
tained by successive Diels–Alder additions of cyclopen-
tadienones and alkynes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
The development of scanning-tunneling microscopes has
allowed not only for imaging at the atomic scale, but also
manipulation of atoms or molecules. Submolecular spec-
troscopy has opened the way to new experiments and new
measurements on single molecules. In order to carry out
such experiments,[1] we have in the past few years designed
a series of molecular devices, named landers, for which the
active polyaromatic hydrocarbon part is maintained above
the metallic surface by spacers so that the molecular board
is electronically decoupled from the surface. These spacers
also increase the molecular mobility on metallic surfaces,[2]
which permits a controlled molecular manipulation.[3,4]
Furthermore, some of these landers have been designed in
order to dock along surface step edges so that one of the
platforms at the end of the polyaromatic plateau is phy-
sisorbed to the upper terrace. Such geometry has, for in-
stance, allowed the measurement of the electronic contact
between the molecular wire and the electrode (Figure 1).[5]
Moreover, these molecular landers have revealed interest-
ing surface restructuring properties. For instance, these
molecules can create trenches in the surface by stabilization
or creation of vacancies in the substrate.[6,7] Alternatively,
Figure 1. General concept of a 2D-lander connected at the step
edge of a metallic surface.
we have also shown that some landers could be used as
molecular molds or templates for the fabrication of small
metallic wires at the Cu(110) step edges,[8] and that the
shape of these nanostructures could be controlled by the
design of the molecular molds.[9] This molding property can
also be used to transport metallic atoms on a surface.[10]
These concepts have been recently extended to 2D landers
from the hexaperi-benzocoronene (HBC) family[11] with the
objective to gain insight into the electron transport in a 2D
molecule and to study molding effects on larger polyarom-
atic hydrocarbons.
In order to further extend these experiments of contact
and molding to very large systems, we have designed a poly-
cyclic aromatic hydrocarbon (PAH) shown in Figure 2. The
“superacene” lander[12] comprises a 72 carbon atom planar
main board partially surrounded by 6 tert-butyl spacers.
The connecting part, left unsubstituted to allow contact
with the upper terrace, is now larger than in previous land-
ers in order to reduce the molecule-to-metal surface contact
resistance.
[a] NanoSciences Group, CEMES-CNRS,
B. P. 93447, 29 Rue J. Marvig, 31055 Toulouse, France
Fax: +33-5-62-25-79-99
E-mail: gourdon@cemes.fr
[b] Current address: Department of Organic Chemistry, Indian As-
sociation for the Cultivation of Science,
Jadavpur, Kolkata 700 032, India
[c] Current address: Chembiotek Research Pvt. Ltd, Block-Bn,
Plot-7, Sector-V, Salt Lake Electronic Complex,
Calcutta 700 091, India
[d] Current address: National Institute for Nanotechnology, De-
partment of Chemistry, University of Alberta,
ECERF: 9107-116 Street, Edmonton, AB T6G 2V4, Canada
136
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 136–140

Synthesis of a 2D Lander
FULL PAPER
been described.[12] In the case of 1, some supplementary
difficulties arise: First, the molecule is partially asymmetric
which increases the number of steps of the synthesis. In-
deed, the elegant new route proposed by Mullen et al.[12c]
which requires a double Diels–Alder reaction on a ther-
mally unstable biscyclopentadienone cannot be extrapo-
lated to asymmetric systems. Second, as the connecting part
of the molecule must be left unsubstituted, the cyclodehy-
drogenation conditions cannot be too harsh to prevent
scrambling of the tert-butyl groups around the polyaro-
matic core. Finally, the reduced number of bulky substitu-
ents increases the compound’s insolubility.
The synthesis requires the preparation of known 2,2Ј-di-
ethynylbiphenyl (3) which was described so far by tedious
and low yield routes. For instance, the preparation from
phenanthrenequinone requires 5 steps with a total yield of
8.5%.[15] This is why we have devised an alternative route
Figure 2. Superacene 2D lander with polyaromatic main board and
tert-butyl spacers.
Results and Discussion
The synthesis of 1, outlined in Scheme 1, uses the syn- for its preparation from biphenyl-2,2Ј-dicarbaldehyde which
thetic concept reported by Müllen et al. for the preparation can be obtained in nearly quantitative yield by Swern oxi-
of extremely extended PAH.[13] The key step of their syn- dation of commercial (2Ј-hydroxymethyl-biphenyl-2-yl)-
thetic routes is the intramolecular oxidative cyclodehydro- methanol.[16] Attempts to directly prepare alkyne 3 by a
genation of suitable oligophenylene precursors (in our case one-pot Wittig-type condensation with dibromomethyltri-
9) under modified Kovacic[14] conditions (Scheme 1, Step phenylphosphonium bromide in the presence of potassium
g). Similar polyaromatic “superacenes”, unsubstituted or tert-butoxide[17] was unsuccessful and gave only low yields
with 8 tert-butyl or dodecyl substituents, have previously of the target product; therefore, the Corey–Fuchs conver-
Scheme 1. Route to 1: (a) CBr4, PPh3, Zn, CH2Cl2 (98%); (b) LDA, THF (78%); (c) i) nBuLi, THF ii) TIPSCl (57%); (d) Diphenyl
ether, microwave irradiation (70%); (e) TBAF/THF, CH2Cl2 (84%); (f) Diphenyl ether (60%); (g) FeCl3, CH3NO2, CH2Cl2, argon bub-
bling (61%).
Eur. J. Org. Chem. 2007, 136–140
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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137

C. Basu, C. Barthes, S. K. Sadhukhan, N. K. Girdhar, A. Gourdon
Finally, although the cyclodehydrogenation conditions
FULL PAPER
sion was preferred. This reaction gave 2,2Ј-bis(2,2-dibromo-
ethenyl)biphenyl 2 in nearly quantitative yield. The second have been maintained as mild as possible, one cannot ex-
step of the sequence afforded diethynyl 3 in 78% yield; the clude some scrambling of the tert-butyl group during this
total yield over the 3-step procedure is now 69% from the last step. Although there is not absolute proof, the weakness
commercial product. The next reaction is the protection of of the mass spectrum peaks [M – C4H9]+ (Ͻ5% of the
one of the ethynyl groups with the bulky triisopropylsilyl maximum intensity, similar to what was observed in the
group which is known to prevent Diels–Alder addition. The same DCI MS conditions for fully substituted octa-tert-bu-
silylation was carried out by metalation with n-butyllithium tyl analogue of 1 and corresponding to fragmentation of
followed by the reaction with triisopropylsilyl chloride to the molecular parent ion) indicates that the mobility of the
give the monoprotected adduct in 57% yield. Then, Diels– tert-butyl groups is not too high in this last step of the ex-
Alder addition under microwave irradiation with activated perimental sequence.
diene 5, with subsequent in situ decarbonylation and aro-
Work in progress is engaged toward UHV STM studies
matization, furnished protected alkyne 6 in 70% yield. The of the electronic and nanopatterning properties of this com-
remaining ethynyl group was then deprotected by moist tet- pound.
rabutylammonium fluoride in THF to obtain free alkyne 7
in 84% yield. The second Diels–Alder reaction furnishing
Experimental Section
polyphenyl 9 (microwave irradiation, 60% yield) required
the preparation of 2,5-bis(4-tert-butylphenyl)-3,4-diphenyl-
cyclopenta-2,4-dien-1-one 8, which was made by condensa-
tion of benzil with 1,3-bis(4-tert-butylphenyl)-2-propenone
(85% yield). The final step is the cyclodehydrogenation of
9, with the creation of 12 C–C bonds and the corresponding
removal of 24 hydrogen atoms. It was carried out by iron
chloride in a 1:1 mixture of dry dichloromethane and nitro-
methane. This final step proved difficult because of the very
low solubility of the reaction intermediates and the risks of
chlorination of the PAH plateau. The reaction was therefore
carried out at small concentrations, with a large excess of
iron chloride, and a constant and efficient flow of argon
was bubbled through the mixture during the 5 d reaction.
As final product 1 is significantly less soluble than the reac-
tion byproducts, namely mono- and dichlorinated adducts
and incompletely cyclodehydrogenated intermediates, the
purification was done by successive washing/centrifugation
steps. The final purity of the product was confirmed by
comparison of the experimental and calculated DCI mass
spectra, and the absence of peaks at m/z Ͼ 1231 (Figure 3).
Indeed, traces of these more soluble and more easily de-
sorbed impurities are immediately apparent in the mass
spectra when present. Because of dynamic aggregation of
this compound in solution, the proton NMR spectra
showed overlapping broad resonances which prevents the
use of this technique to attest the compound’s purity.
1
General:. H- and 13C NMR spectra were recorded with a Bruker
WF-250 in CDCl3 or CD2Cl2 solutions at 20 °C and internal stan-
dard (CDCl3 at δH: 7.25 ppm, δC: 77.0 ppm, CD2Cl2 at δH:
5.30 ppm, δC: 53.8 ppm). Mass Spectroscopy was performed with
a Nermag R10-R10 (DCI). Elemental analyses were done by the
Service d’Analyse de l’ICSN (Paris) and by the Service d’Analyse
du LCC (Toulouse). 2,3,4,5-Tetrakis(4-tert-butylphenyl)cyclopenta-
2,4-dien-1-one (5) was prepared according to the literature.[11] THF
was distilled from Na/benzophenone. Dichloromethane was dis-
tilled from calcium hydride and nitromethane was dried with mo-
lecular sieves. Other solvents and reagents were used as obtained
in the best quality available. The microwave heating was carried
out in closed vials with a CEM-Discover monomode microwave
apparatus at 300 watts under the conditions (temperature, time)
given here. After completion of the reaction, the vessel was cooled
down rapidly to 60 °C
Compound 2,2Ј-Bis(2,2-dibromoethenyl)biphenyl (2): A mixture of
CBr4 (10 g, 30.15 mmol), PPh3 (7.909 g, 30.15 mmol), and Zn dust
(1.972 g, 30.15 mmol) in dry dichloromethane (100 mL) was stirred
at room temp. for 24 h. The suspension was then cooled to 0 °C
and biphenyl-2,2Ј-dicarbaldehyde (600 mg, 2.85 mmol) in dry
dichloromethane (20 mL) was added. The suspension was then
stirred for 24 h at room temp. under an atmosphere of argon. The
suspension was then filtered and the precipitate was washed with
dichloromethane (25 mL). After evaporation of the combined fil-
trates, the residue was dissolved in dichloromethane (30 mL) and
then hexane was added to precipitate the remaining P-containing
products. The suspension was filtered through celite and the residue
washed with hexane (2ϫ75 mL). The filtrates were evaporated and
the oily residue was chromatographed on silica gel with the use of
dichloromethane/petroleum ether (1:1) as the eluent. Yield: 1.481 g
(98%). 1H NMR (250 MHz, CD2Cl2): δ = 7.04 (s, 2 H, vinyl), 7.20–
7.26 (m, 2 H, arom), 7.40–7.48 (m, 4 H, arom), 7.71–7.78 (m, 2 H,
arom) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 140.18, 137.06,
135.68, 130.90, 129.58, 129.17, 128.52, 92.14 ppm. MS (DCI, NH3)
m/z = 539.8 [M + NH4]+. C16H10Br4 (521.87): calcd. C 36.82, H
1.93; found C 36.5, H 1.7.
Compound 2,2Ј-Diethynylbiphenyl (3): LDA (1.8  in THF, 3.4 mL)
was slowly added to a solution of 2 (400 mg, 0.77 mmol) in THF
(30 mL) at –78 °C. After one hour stirring at this temperature, the
mixture was left to warm up to room temp, and the stirring was
then continued for another 2 h. The reaction was then quenched
by the addition of a saturated NH4Cl solution (20 mL), and the
mixture was diluted with hexane (100 mL). The organic phase was
Figure 3. Comparison of the experimental (dashed bars) and calcu-
lated (grey bars) DCI mass spectrum (parent ion [M]+) of com-
pound 1.
138
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Eur. J. Org. Chem. 2007, 136–140

Synthesis of a 2D Lander
FULL PAPER
then washed with water (2ϫ50 mL), dried with magnesium sulfate,
filtered, and the solvents evaporated. Preparative chromatography
over silica gel with the use of dichloromethane/hexane (1:2) as the
eluent gave 120 mg of 3 (yield: 78%). 1H- and 13C NMR, MS,
melting point, and chemical analysis are consistent with those pre-
sented in ref.[15]
nol (5 mL) was added a solution of KOH (2  in dry ethanol,
2 mL). The solution was heated at reflux for 5 h and then cooled
to 0 °C. The dark crystalline product was filtered, washed with cold
ethanol (2ϫ1 mL), and dried under vacuum to afford the pure
product. Yield: 1.8 g, 85%. 1H NMR (250 MHz, CD2Cl2): δ = 1.29
(s, 18 H, tBu), 6.94–7.00 (m, 4 H, arom), 7.13–7.21 (m, 6 H, arom),
7.21–7.33 (m, 8 H, arom) ppm. 13C NMR (62.5 MHz, CDCl3): δ =
31.24, 34.56, 124.84, 125.00, 127.75, 128.28, 129.32, 129.66, 133.39,
150.29, 153.92, 201.10 ppm. C37H36O (496.68): calcd. C 89.47, H
7.31; Found C 89.1, H 7.7. MS (DCI, NH3): m/z = 514 [M +
NH4]+.
[(2Ј-Ethynylbiphenyl-2-yl)ethynyl](triisopropyl)silane (4): nBuLi
(2.5  in hexane, 0.68 mL,1.36 mmol) was added to a stirred solu-
tion of 2,2Ј-diethynylbiphenyl 3 (250 mg, 1.23 mmol) in THF at
–78 °C. The reaction mixture was then stirred at this temperature
for 2 h. Triisopropylsilyl chloride (0.4 mL, 1.85 mmol) was then
added, and the solution was warmed up to room temp. and stirred
for another 2 h. The reaction was quenched by the dropwise ad-
dition of water, and the solvent was removed under vacuum. The
residue was then extracted with dichloromethane. The organic layer
was washed with water, dried with MgSO4, and the solvents evapo-
rated. The residue was purified by flash chromatography (5%
dichloromethane in petroleum ether) to afford the pure product.
Compound 9: A mixture of 6 (50 mg, 0.0638 mmol) and 2,5-
bis(4-tert-butylphenyl)-3,4-diphenylcyclopenta-2,4-dien-1-one (8)
(38.4 mg, 0.052 mmol) in diphenyl ether (1.5 g) was stirred at
160 °C under microwave irradiation (300 w) for 45 min. The reac-
tion mixture was then cooled, diluted in dichloromethane (1 mL),
and poured into stirred methanol (50 mL). The solid was filtered
and washed with methanol, dried under vacuum, and recrystallized
from dichloromethane/ethanol (1:9). Yield: 60%. 1H NMR
(250 MHz, CD2Cl2): δ = 1.01 (s, 9 H, tBu), 1.08 (s, 9 H, tBu), 1.13
(s, 9 H, tBu), 1.23 (s, 9 H, tBu), 1.53 (s, 18 H, tBu), 6.56–7.20 (m,
40 H, arom), 7.30–7.36 (m, 1 H, arom), 7.44–7.54 (m, 3 H, arom)
ppm. 13C NMR (62.5 MHz, CDCl3): δ = 31.18, 34.23, 118.86,
122.70, 123.06, 123.75, 123.89, 124.04, 125.01, 125.30, 125.46,
125.63, 125.95, 126.09, 126.69, 130.17, 130.61, 130.72, 131.06,
131.35, 131.96, 132.39, 132.96, 133.19, 133.82, 133.90, 134.16,
134.53, 136.85, 136.99, 138.00, 138.53, 138.90, 139.49, 139.64,
140.28, 140.36, 141.03, 141.62, 142.93, 147.63, 147.86, 148.11,
148.34, 148.60 ppm. C96H98 (1251.81): calcd. C 92.11, H 7.89;
found C 91.9, H 7.5. MS (DCI, NH3): m/z = 1269 [M + NH4]+.
1
Yield: 252 mg, 57%. H NMR (250 MHz, CDCl3): δ = 0.95 (s, 21
H, TIPS), 2.99 (s, 1 H, CC-H), 7.33–7.39 (m, 6 H, arom), 7.54–
7.59 (m, 2 H, arom) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 11.14,
18.50, 79.95, 82.74, 93.94, 105.68, 121.54, 122.99, 127.16, 127.28,
127.72, 128.22, 129.75, 130.13, 132.70, 132.92, 143.21, 143.65 ppm.
C25H30Si (358.59): calcd. C 83.74, H 8.43; found C 84.1, H 8.2. MS
(DCI, NH3): m/z = 376 [M + NH4]+.
Compound 6: A mixture of 4 (50 mg, 0.14 mmol) and tetrakis(4-
tert-butylphenyl)cyclopenta-2,4-dien-1-one (5) (84.9 mg, 0.14 mmol)
in diphenyl ether (1.5 g) was stirred at 160 °C under microwave
irradiation for 45 min. The cooled reaction mixture was then
poured in stirred methanol (50 mL). The precipitated white product
was filtered, washed with methanol, and recrystallized from 10%
dichloromethane in methanol. Yield: 92 mg, 70%. 1H NMR
(250 MHz, CD2Cl2): δ = 0.84–0.87 (m, 21 H, TIPS), 1.09 (s, 9 H,
tBu), 1.12 (s, 9 H, tBu), 1.16 (s, 9 H, tBu), 1.21 (s, 9 H, tBu), 6.72
(d, 4 H, J = 8.5 Hz, arom), 6.96–7.12 (m, 10 H, arom), 7.14–7.36
(m, 10 H, arom), 7.61–7.66 (m, 1 H, arom) ppm. 13C NMR
(62.5 MHz, CDCl3): δ = 11.14, 18.47, 31.17, 34.06, 94.13, 106.46,
122.77, 123.18, 123.84, 125.83, 126.15, 126.37, 127.34, 129.41,
129.78, 130.47, 131.10, 131.82, 132.12, 132.38, 137.14, 137.80,
138.58, 138.80, 139.33, 140.05, 142.06, 147.72, 147.88 ppm.
C69H82Si (939.47): calcd. C 88.21, H 8.80; found C 88.11, H 8.80.
MS (DCI, NH3): m/z = 956 [M + NH4]+.
Superacene 1: A solution of FeCl3 (607 mg, 3.74 mmol) in dry ni-
tromethane (10 mL) was added dropwise to a solution of 9 (20 mg,
0.0159 mmol) in dry dichloromethane (10 mL) with a strong flow
of argon in the solution. The reaction mixture was stirred for 5 d
with regular addition of a 1:1 mixture of dry dichloromethane and
dry nitromethane to maintain a constant volume. The reaction was
quenched with methanol (20 mL), and the solvent was evaporated
under vacuum. A few drops of water were added to the deep red-
dish gummy material. The brownish–yellow solid was suspended
and centrifuged successively with methanol and water to give the
desired product as a yellow powder. Yield: 30 mg, 61%. MS (DCl,
NH3): m/z (%) = 1225 (3.7), 1226 (12.4), 1227 (100), 1228 (99.1),
1229 (52.9), 1230 (14.5), 1231 (2.5). C96H74 (1227.61): calcd. C
93.92, H 6.08; found C 93.6, H 5.8.
Compound 7: Tetrabutylammonium fluoride [1  solution in THF
(5% water), 0.5 mmol] was added to a solution of 6 (200 mg,
0.212 mmol) in CH2Cl2 (15 mL), heated under reflux for 2 h, co-
oled, diluted with CH2Cl2 (10 mL), and washed with water
(3ϫ20 mL). The organic layer was dried with MgSO4 and the sol-
vents evaporated. The residue was purified by flash chromatog-
raphy (silica gel, 5% CH2Cl2 in petroleum ether) to afford the pure
product. Yield: 140 mg, 84%. 1H NMR (250 MHz, CD2Cl2): δ =
1.04 (s, 9 H, tBu), 1.08 (s, 9 H, tBu), 1.13 (s, 9 H, tBu), 1.24 (s, 9
H, tBu), 3.9 (s, 1 H, C2-H), 6.41–6.50 (m, 2 H, arom), 6.64–6.96
(m, 10 H, arom), 6.97–7.44 (m, 11 H, arom), 7.46–7.54 (m, 2 H,
arom) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 31.66, 34.76, 80.83,
84.09, 122.79, 123.69, 124.16, 124.91, 126.82, 127.26, 127.57,
128.51, 130.17, 131.40, 131.74, 132.77, 133.37, 133.74, 137.47,
138.19, 138.47, 139;69, 140.21, 141.60, 142.66, 148.45, 148.72,
149.08, 149.52 ppm. C60H62 (783.13): calcd. C 92.02, H 7.98; found
C 91.8, H 8.2. MS (DCI, NH3): m/z = 800 [M + NH4]+.
Acknowledgments
This work was supported by the CNRS, the European Community
FET-NID projects BUN (Bottom-Up Nanomachines) IST-1999-
11565 and CHIC (Consortium for Hamiltonian Intramolecular
Computing) IST-2001-33578.
[1] F. Moresco, A. Gourdon, Proc. Natl. Acad. Sci. USA 2005,
102, 8809–8814.
[2] R. Otero, F. Hummelink, F. Sato, S. Legoas, P. Thorstrup, E.
Laegsgaard, I. Stensgaard, D. Galvao, F. Besenbacher, Nat.
Mater. 2004, 3, 779–782.
[3] M. Alemani, L. Gross, F. Moresco, K.-H. Rieder, C. Wang, X.
Bouju, A. Gourdon, C. Joachim, Chem. Phys. Lett. 2005, 402,
180–185.
[4] L. Grill, F. Moresco, P. Jiang, C. Joachim, A. Gourdon, K.-H.
Rieder, Phys. Rev. B 2004, 69, 035416 (7 pages).
2,5-Bis(4-tert-butylphenyl)-3,4-diphenylcyclopenta-2,4-dien-1-one
(8): To a boiling solution of benzil (0.911 g, 4.34 mmol) and 1,3-
bis(4-tert-butylphenyl)-2-propenone (1.4 g, 4.34 mmol) in dry etha-
Eur. J. Org. Chem. 2007, 136–140
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
139

C. Basu, C. Barthes, S. K. Sadhukhan, N. K. Girdhar, A. Gourdon
FULL PAPER
[5] L. Grill, F. Moresco, K.-H. Rieder, S. Stojkovic, A. Gourdon,
C. Joachim, Nano Lett. 2005, 5, 859–863.
Chem. 1997, 109, 1675–1679; b) V. S. Iyer, M. Wehmeier, J. D.
Brand, M. A. Keegstra, K. Müllen, Angew. Chem. Int. Ed.
Engl. 1997, 36, 1604–1607; Angew. Chem. 1997, 109, 1679–
1682; c) D. Wasserfallen, M. Kastler, W. Pisula, W. A. Hofer,
Y. Fojel, Z. Wang, K. Müllen, J. Am. Chem. Soc. 2006, 128,
1334–1339.
[6] L. Gross, F. Moresco, M. Alemani, H. Tang, A. Gourdon, C.
Joachim, K.-H. Rieder, Chem. Phys. Lett. 2003, 371, 750–756.
[7] a) M. Schunack, L. Petersen, A. Kuhnle, E. Laegsgaard, I.
Stensgaard, I. Johannsen, F. Besenbacher, Phys. Rev. Lett.
2001, 86, 456–459; b) M. Schunack, E. Laegsgaard, I.
Stensgaard, I. Johannsen, F. Besenbacher, Angew. Chem. Int.
Ed. 2001, 40, 2623–2626; Angew. Chem. 2001, 113, 2693–2696.
[8] F. Rosei, M. Schunack, P. Jiang, A. Gourdon, E. Laegsgaard,
I. Stensgaard, C. Joachim, F. Besenbacher, Science 2002, 296,
328–331.
[9] R. Otero, F. Rosei, Y. Naitoh, P. Jiang, P. Thostrup, A.
Gourdon, E. Laegsgaard, I. Stensgaard, C. Joachim, F. Besen-
bacher, Nano Lett. 2004, 4, 75–78.
[10] L. Gross, K.-H. Rieder, F. Moresco, S. Stojkovic, A. Gourdon,
C. Joachim, Nat. Mater. 2005, 4, 892–895.
[13] a) M. Müller, C. Kübel, F. Morgenroth, V. S. Iyer, K. Müllen,
Carbon 1998, 36, 827–831; b) F. Morgenroth, C. Kübel, M.
Müller, U. M. Wiesler, A. J. Berresheim, M. Wagner, K.
Müllen, Carbon 1998, 36, 833–837.
[14] P. Kovacic, M. B. Jones, Chem. Rev. 1987, 87, 357–379.
[15] M. Sarobe, R. van Heerbeek, L. W. Jenneskens, J. W. Zwikker,
Liebigs Ann./Recueil 1997, 2499–2503.
[16] A. G. J. Ligtenbarg, E. K. van der Beuken, A. Meetsma, N.
Veldman, W. J. J. Smeets, A. L. Spek, B. L. Feringa, J. Chem.
Soc., Dalton Trans. 1998, 263–270.
[17] P. Michel, D. Gennet, A. Rassat, Tetrahedron Lett. 1999, 40,
8575–8578.
[11] S. K. Sadhukhan, C. Viala, A. Gourdon, Synthesis 2003, 10,
1521–1525.
Received: August 1, 2006
[12] a) M. Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen,
Angew. Chem. Int. Ed. Engl. 1997, 36, 1607–1610; Angew.
Published Online: October 13, 2006
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