Synthesis of polyaromatic hydrocarbons with a central rotor

Article abstract of DOI:10.1002/1099-0690(200212)2002:24<4185::AID-EJOC4185>3.0.CO;2-Z

A series of molecular landers comprising a central mobile part has been synthesised. The two rigid main boards consist of acenaphtho[1,2-k]fluoranthene groups, each substituted in positions 7 and 14 by 3,5-di-tert-butylphenyl groups. The boards are linked by a diethynylanthracene, a phenyl, or a biphenyl rotor. ( Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2002).

Full text of DOI:10.1002/1099-0690(200212)2002:24<4185::AID-EJOC4185>3.0.CO;2-Z

FULL PAPER
Synthesis of Polyaromatic Hydrocarbons with a Central Rotor
[a]
Christine Viala,[a] Andrea Secchi,#[a] and Andre Gourdon*
´
Keywords: Molecular devices / Fused-ring systems / Cross-coupling / Single-molecule studies
A series of molecular landers comprising a central mobile
part has been synthesised. The two rigid main boards consist
of acenaphtho[1,2-k]fluoranthene groups, each substituted in
positions 7 and 14 by 3,5-di-tert-butylphenyl groups. The
boards are linked by a diethynylanthracene, a phenyl, or a
biphenyl rotor.
( Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim,
Germany, 2002)
Introduction
The development of nanoelectronic devices using single
molecules calls for a better understanding of the electrical
and mechanical properties of isolated molecules.[1,2] Since
the early 1990s, the development of Scanning Tunneling
Microscopy has allowed not only imaging of molecules but
also exploration of molecular electrical,[3] mechanical,[4,5]
and chemical[6,7] properties on an individual non-statistical
basis.
We have recently designed specific molecules, which are
named landers by analogy with landing craft, such as the
Mars lander, for the study of electron transport along a
single molecular wire in a UHV-STM tip-molecule-metallic
surface experiment.[8] These molecules comprise a rigid po-
Scheme 1. General scheme of a lander with rotor
currently extending this study to systems in which the mo-
bile part is incorporated within the core of the molecule so
that the electrons tunnel through the rotor.
˚
lyaromatic board, which can be maintained several A above
a surface by appropriate spacers (legs), in order to prevent
direct electron flow between the tip and the surface
through, and perpendicular to, the board plane. In order to
minimize electron leaks, the spacers must show little elec-
tronic coupling with the board and with the metal. This
device has allowed us to measure for the first time the spa-
tially resolved conductance of a single molecular wire.[9]
Molecular landers can also be used as templates to accom-
modate metal atoms at the step edges of a metal substrate,
and for moulding metallic nanowires.[10] This work is being
extended to the study of single molecular switches, i.e. mole-
cules for which the conductance can be controlled by an
external action (Scheme 1).
Any modification of the angle between the planes of the
main boards and the rotor plane will have a large impact
on the longitudinal conductance of the molecule, as it alters
the electronic coupling between these components. There-
fore, manipulation of the rotor conformation by the STM
tip could lead to a switching effect. We have also envisaged
using this type of device to study the influence of the inel-
astic part of the tunnelling current on the movement of the
central rotor. As the tunnel current passes through the mo-
lecule, the internal temperature increases by inelastic ab-
sorption, thus populating higher energy rotational modes.
Fine analysis of the tunnel noise should show this variation
of internal motion.
We have recently been able to fully control the conforma-
tional changes of a single molecule by STM,[11] by using
the tip to reversibly induce the rotation of an external part
of the molecule, thus modifying its electronic properties and
thereby realizing a conformational molecular switch. We are
Results and Discussion
We have carried out the syntheses of several landers de-
signed according to the above architecture and shown in
Scheme 2.
[a]
´
Groupe Electronique Moleculaire, Cemes/CNRS,
B. P. 4347, 29 Rue J. Marvig, 31055 Toulouse Cedex 4, France,
Fax: (internat.) ϩ 33-5/62257999
E-mail: gourdon@cemes.fr
From previous studies,[12] it was found that the 7,14-
bis(3,5-di-tert-butylphenyl)acenaphtho[1,2-k]fluoranthene
[b]
`
Dipartimento di Chimica Organica e Industriale dell’Universita
Viale delle Scienze 17/a, 43100 Parma, Italy
Eur. J. Org. Chem. 2002, 4185Ϫ4189  2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/02/1224Ϫ4185 $ 20.00ϩ.50/0
4185

C. Viala, A. Secchi, A. Gourdon
FULL PAPER
molecule manipulation and stabilisation of the molecule on
step edges at lower temperatures.
For these studies, three compounds with different types
of rotors were synthesized: one with a low energy rotation
barrier comprising diethynylanthracene, one with a phenyl
and one with a biphenyl moiety. Attempts to transfer 1 to
the substrate by sublimation in an STM chamber showed
that this molecule could often not withstand the process
under UHV conditions, due to thermal decomposition dur-
ing sublimation and/or reaction with the bare metallic sur-
face. This led us to prepare molecules such as 2 and 3,
which have higher rotation barriers than 1 but which have
more robust rotors and better thermal stability on bare me-
tallic surfaces.
The synthesis of the main-board molecule is shown in
Scheme 3. The first step is the preparation of 1,3-bis(3,5-di-
tert-butylphenyl)propan-2-one (4) by reaction of 1-(bromo-
methyl)-3,5-di-tert-butylbenzene with tosylmethyl isocyan-
ide followed by hydrolysis.[13] The best yields (45%) were
obtained using dry DMF as solvent and NaH as base at
room temperature. This route is more practical than car-
bonylation[8] with toxic Fe(CO)5 or Fe2(CO)9 which also
requires a difficult separation of iron hydroxide from the
aqueous suspension.
Scheme 2. Landers with a rotor
board is suitable for the terminal parts of the device. Des-
pite important distortions of the spacers on metallic sur-
faces, the central core is rigid and maintained above the
surface at distances which are large enough that there is
little electronic coupling with the metal, owing to the steric
crowding and insulating properties of the di-tert-bu-
tylphenyl substituents (Figure 1).
Scheme 3. Synthesis of the main board: (a) TosMIC, NaH, DMF;
HCl, CH2Cl2, 45%; (b) KOH, MeOH, 92%; (c) o-xylene or toluene;
(d) DDQ, CH2Cl2
Subsequently, a double Knoevenagel condensation with
bromoacetophenone[14] in methanol/KOH gave the cyclo-
pentadienone 5 in good yield (92%). Reaction with acen-
aphthylene, decarbonylation, and rearomatization gave, de-
pending on the reaction conditions, 6 and/or 7. In refluxing
toluene, the reaction was slow (3 d) and yielded first 7 and,
by in situ air oxidation, 6. In o-xylene, the reaction was
faster (1 d) and yielded exclusively 6. Alternatively, 7 could
Figure 1. Perspective view of a CPK model of 1 showing the min-
imum energy conformation under vacuum; the di-tert-butylphenyl
spacers’ planes are maintained nearly perpendicular to the main
board plane by steric crowding
Similar molecules show a rather low diffusion barrier be oxidized by DDQ/dichloromethane in quantitative
with some mobility at low temperatures, allowing a single yields.
4186
Eur. J. Org. Chem. 2002, 4185Ϫ4189

Synthesis of Polyaromatic Hydrocarbons with a Central Rotor
FULL PAPER
The synthesis of 1 was then carried out as shown in
Scheme 4. The alkynyl precursor 8 was obtained in 91%
yield by palladium coupling of 6 and 2-methyl-3-butyn-2-ol
using Crisp’s procedure.[15] Retro Favorsky elimination of
acetone from 8 by tBuOK in refluxing THF gave the alkyne
9 in good yield (92%). Sonogashira coupling with 9,10-di-
iodoanthracene under Linstrumelle conditions[16] then pro-
vided the lander 1 as a bright orange powder in 61% yield.
Scheme 5. Synthesis of 2 and 3: Pd2(dba)3, tBu3P, CsF, THF, 41%
(2), 46% (3)
The electronic spectra of compounds 2 and 3 recorded in
CH2Cl2 showed similar absorption bands at relatively low
energy, due to the extended polyaromatic character of the
acenaphtho[1,2-k]fluoranthene groups. For 1, the red shift
of the maximum absorption is attributed to a smaller
HOMOϪLUMO gap by extended conjugation between the
two main boards and the diethynylanthracene group.
All of the compounds 1Ϫ3 are fluorescent in dichlorome-
thane solutions with small (22 nm for 1) to moderate
(42 nm for 2 and 3) Stokes shifts, as expected for relatively
rigid molecules.
Conclusion
Scheme 4. Synthesis of compound 1: (a) 2-methyl-3-butyn-2-ol,
Pd(PPh3)4, PPh3, CuI, LiBr, piperidine, 91%; (b) tBuOK, THF,
92%; (c) Pd(PPh3)2Cl2, CuI, piperidine, THF, 61%
The synthesis of polyaromatic hydrocarbons designed for
the study of intramolecular movements in STM single mo-
lecule surface experiments has been carried out. These mo-
lecular devices comprise two acenaphtho[1,2-k]fluoranthene
main boards, each substituted by two 3,5-di-tert-bu-
tylphenyl spacers to maintain the central part above the me-
tallic surface. These two parts are connected by a central
mobile unit. Work in progress is directed toward UHV-
STM studies of the mechanical and switching properties of
these devices.
The synthetic route to 2 and 3 is given in Scheme 5. It
involves Suzuki coupling of phenyl- and biphenyldiboronic
acid bis(neopentylglycol) cyclic esters 10 and 11 with the
substituted bromoacenaphthofluoranthene 6. The electron-
rich character of 6 hinders the oxidative insertion of Pd0
into the CϪBr bond and prevents efficient catalysis with,
for instance, Pd(PPh3)4. Extensive study of the coupling
conditions led to satisfactory yields (41Ϫ46%) of this
double coupling using 0.47 equiv. of diboronic bis(neopen-
tylglycol) cyclic esters, 1.5 mol % of Pd2(dba)3, 3.5 mol %
of tBu3P and CsF (2 equiv.) in refluxing THF.[17Ϫ19] These
conditions minimise formation of the monocoupled derivat-
ive (less than 15%) and of reduced species, the main by-
product under other reaction conditions.
Experimental Section
General: 1H and 13C NMR spectra were recorded with a Bruker
WF-250 in CDCl3 or CD2Cl2 solutions at 20 °C and internal stand-
ard (CDCl3: δH ϭ 7.25 ppm, δC ϭ 77.0 ppm; CD2Cl2: δH
ϭ
5.30 ppm, δC ϭ 53.8 ppm). Mass spectrometry was performed with
a Nermag R10-R10 (DCI). Elemental analyses were carried out by
Table 1. Spectroscopic properties of 1Ϫ3 in dichloromethane
Compound
Absorption: λmax [nm] (ε ϫ 104 [Ϫ1 cmϪ1])
Emission: λmax [nm] (λexc. [nm])[a]
1
2
3
542 (5.5), 514 (6.12), 319 (8.6)
447 (7.1), 425 (sh.),[b] 317 (12.3)
445 (5.4), 423 (sh.),[b] 319 (9.7)
564, 604 (540)
489, 514 (445)
487, 512 (445)
[a]
[b]
Concentration 10Ϫ6 . sh ϭ shoulder.
Eur. J. Org. Chem. 2002, 4185Ϫ4189
4187

C. Viala, A. Secchi, A. Gourdon
FULL PAPER
the Service d’Analyse de l’ICSN (Paris). 1-(Bromomethyl)-3,5-di-
4 Hz), 7.44 (s, 2 H), 7.36 (d, J ϭ 7.8 Hz, 2 H), 7.27Ϫ7.14 (m, 5 H),
6.73 (d, J ϭ 7.2 Hz, 1 H), 6.49 (d, J ϭ 8.0 Hz, 1 H), 6.22 (d, J ϭ
tert-butyltoluene,[8]
bromoacetophenone,[14]
and
9,10-di-
iodoanthracene[20] were prepared according to published pro- 7.0 Hz, 2 H), 5.29 (br. s, 2 H), 1.42 and 1.33 (2 br. s, 36 H) ppm.
cedures. THF was distilled from Na/benzophenone. Other solvents
and reagents were used as obtained in the best quality available.
13C NMR (CDCl3): δ ϭ 152.5, 150.3, 145.2, 145.1, 140.1, 139.1,
137.1, 136.8, 136.5, 134.8, 131.4, 130.6, 130.4, 130.2, 129.9, 128.5,
127.2, 126.0, 123.0, 121.4, 121.2, 120.9, 119.4, 119.2, 118.5, 50.3,
35.1, 31.6 ppm. MS (DCI, NH3): m/z ϭ 784 [MHϩ].
1,3-Bis(3,5-di-tert-butylphenyl)propan-2-one (4): NaH (0.53 g,
22.1 mmol) was added to a solution of 1-(bromomethyl)-3,5-di-tert-
butylbenzene (5.0 g, 17.7 mmol) and tosylmethyl isocyanide
(TosMIC; 1.7 g, 9 mmol) in dry DMF (25 mL). The resulting het-
erogeneous mixture was stirred overnight at room temperature,
then the solvent was removed under vacuum. The residue was di-
luted with CH2Cl2 (25 mL) and water (50 mL). The separated or-
ganic phase was then treated with a concentrated HCl solution
(37%, 10 mL) for 30 min with vigorous stirring. The organic layer
was then separated, washed neutral with water, dried (MgSO4) and
the solvents were completely evaporated. Purification of the residue
by flash chromatography [light petroleum ether/dichloromethane
(2:1)] provided 1,3-bis(3,5-di-tert-butylphenyl)propan-2-one (4)
(1.72 g, 45%) as a white solid. C31H46O (434.7): calcd. C 85.7, H
Compound 8: A solution of 6 (400 mg, 0.51 mmol), 2-methyl-3-bu-
tyn-2-ol (0.25 mL, mmol), PPh3 (4 mg, 15.2 µmol), and Pd(Ph3)4
(10 mg, 8.6 µmol) in degassed piperidine (20 mL) was treated with
copper iodide (4 mg, 21.0 µmol) and lithium bromide (15 mg,
0.17 mmol) in dry and degassed THF (5 mL). After refluxing for
5 h under argon, the solvents were evaporated from the reaction
mixture. The residue was extracted with dichloromethane (200 mL)
and then washed with 5% HCl (2 ϫ 50 mL) and water (2 ϫ 50
mL). After drying (MgSO4), the solution was concentrated and the
product was purified by column chromatography using dichlorome-
thane as eluent. This yielded the protected alkyne as a yellow pow-
der (361 mg, 91%). C59H60O (785.11): calcd. C 90.26, H 7.70; found
C 89.60, H 7.39. 1H NMR (CDCl3): δ ϭ 7.94 (d, J ϭ 8.5 Hz, 1
H), 7.71 (d, J ϭ 8.5 Hz, 2 H), 7.67 (br. s, 2 H), 7.53 (br. s, 4 H),
7.42 (d, J ϭ 7.25 Hz, 1 H), 7.35Ϫ7.25 (m, 3 H), 6.87Ϫ6.75 (m, 3
H), 6.63 (d, J ϭ 7.25 Hz, 1 H), 2.16 (s, 1 H), 1.68 (s, 6 H), 1.40 (s,
36 H) ppm. 13C NMR (CDCl3): δ ϭ 152.0, 137.7, 137.4, 137.2,
136.9, 136.5, 135.3, 133.2, 133.0, 132.0, 129.5, 128.2, 127.6, 126.3,
124.6, 123.6, 123.4, 122.5, 121.1, 119.2, 99.0, 65.9, 35.1, 31.5 ppm.
MS (DCI, NH3): m/z ϭ 728 [MHϩ].
1
10.7; found C 85.4, H 10.9. H NMR (CD2Cl2): δ ϭ 7.31 (t, J ϭ
1.9 Hz, 2 H), 7.0 (d, J ϭ 1.9 Hz, 4 H), 3.73 (s, 4 H), 1.32 (s, 36 H)
ppm. 13C NMR (CDCl3): δ ϭ 206.5, 151.1, 133.3, 123.7, 120.9,
49.5, 34.8, 31.5 ppm. MS (DCI, NH3): m/z ϭ 435 [MHϩ].
3-Bromo-7,9-bis(3,5-di-tert-butylphenyl)-8H-cyclopenta[a]-
acenaphthylen-8-one (5): A 1  solution of KOH in methanol (1
mL) was added dropwise to a suspension of 1,3-bis(3,5-di-tert-bu-
tylphenyl)propan-2-one (4; 500 mg, 1.15 mmol) and 5-bromoacen-
aphthylene-1,2-dione (300 mg, 1.15 mmol) in methanol (10 mL).
After stirring for 4 h at room temperature, the resulting dark green
heterogeneous mixture was filtered and the precipitate was washed
twice with small portions of methanol. Further drying under va-
cuum provided 0.7 g (92%) of compound 5 as a dark-green solid.
Compound 9: A solution of the alcohol 8 (100 mg, 0.13 mmol) in
dry and degassed THF (100 mL) was treated with tBuOK (30 mg,
0.267 mmol), then refluxed under argon for 0.5 h. After evapora-
tion of the solvents under vacuum, the residue was extracted with
dichloromethane (100 mL), washed with water (2 ϫ 25 mL), and
passed though a short plug of silica gel. Yield 87 mg (92%). The
product is stable when stored in the dark at Ϫ30 °C. C56H54
(727.03): calcd. C 92.5, H 7.5; found C 91.1, H 7.8. 1H NMR
(CD2Cl2): δ ϭ 8.01 (d, J ϭ 7.8 Hz, 1 H), 7.77Ϫ7.73 (m, 4 H),
7.54Ϫ7.50 (m, 5 H), 7.42Ϫ7.32 (m, 3 H), 6.85Ϫ7.78 (m, 3 H), 6.70
(d, J ϭ 7.25 Hz, 1 H), 1.50 (br. s, 36 H) ppm. 13C NMR (CDCl3):
δ ϭ 152.01, 137.70, 137.36, 136.98, 136.51, 135.20, 132.97, 132.75,
128.43, 127.65, 126.37, 124.58, 123.68, 123.36, 122.33, 121.17,
118.54, 82.14, 81.60, 35.15, 31.52 ppm. MS (DCI, NH3): m/z ϭ
786 [MHϩ].
1
C43H47BrO (659.74): calcd. C 78.3, H 7.2; found C 78.9, H 7.4. H
NMR (CDCl3): δ ϭ 8.11 (d, J ϭ 7.1 Hz, 1 H), 8.04 (d, J ϭ 8 Hz,
1 H), 7.91 (d, J ϭ 7.7 Hz, 1 H), 7.82 (d, J ϭ 7.7 Hz, 1 H),
7.71Ϫ7.64 (m, 5 H), 7.48 (t, J ϭ 1.5 Hz, 2 H), 1.41 (s, 36 H) ppm.
13C NMR (CDCl3): δ ϭ 202.0, 152.7, 152.2, 150.8, 145.0, 132.1,
131.6, 131.6, 130.3, 129.4, 126.5, 123.3, 123.2, 123.0, 122.7, 122.3,
121.3, 120.8, 35.0, 31.4 ppm. MS (DCI, NH3): m/z ϭ 660 [MHϩ].
3-Bromo-7,14-bis(3,5-di-tert-butylphenyl)acenaphtho[1,2-k]-
fluoranthene (6): A solution of the cyclopentadienone derivative 5
(0.5 g, 0.76 mmol) and acenaphthylene (80%, 0.14 g, 0.76 mmol) in
o-xylene (10 mL) was refluxed for 24 h, then the solvent was com-
pletely removed under vacuum. Purification of the resulting sticky
residue by flash chromatography [light petroleum ether/dichloro-
methane (9:1)] afforded compound 6 (0.48 g, 80%) as a yellow
solid. C54H53Br (781.90): calcd. C 82.95, H 6.8; found C 82.6; H
Compound 1: A solution of 9 (100 mg, 0.137 mmol) in degassed
piperidine (10 mL) and THF (2 mL) was treated with 9,10-di-
iodoanthracene (25 mg, 58.1 µmol), dichlorobis(triphenylphos-
phane)palladium (5 mg, 7.1 µmol) and copper iodide (5 mg, 15.7
µmol). After refluxing for 1 h under argon, the solvents were evap-
orated under vacuum and the residue was extracted with dichloro-
methane (100 mL). The solution was washed with 10% aqueous
ammonia, water and 5% aqueous hydrochloric acid, then washed
with water to neutrality and dried with magnesium sulfate. Flash
chromatography using petroleum ether/dichloromethane (1:8) as
eluent gave the product as a bright orange solid. Yield 57 mg (61%).
1
7.1. H NMR (CDCl3): δ ϭ 7.87 (d, J ϭ 8.4 Hz, 1 H), 7.74Ϫ7.67
(m, 4 H), 7.53Ϫ7.50 (m, 5 H), 7.38Ϫ7.34 (m, 3 H), 6.81Ϫ6.75 (m,
3 H), 6.53 (d, J ϭ 7.6 Hz, 2 H), 1.41 (m, 36 H). 13C NMR
(CD2Cl2): δ ϭ 152.5, 137.8, 137.3, 136.9, 136.7, 135.5, 134.7, 133.4,
131.3, 129.9, 129.6, 129.2, 128.0, 126.7, 125.6, 124.2, 124.0, 123.7,
123.5, 121.9, 35.4, 31.6 ppm. MS (DCI, NH3): m/z ϭ 781 [MHϩ].
Alternatively, after removal of the solvent under reduced pressure,
the desired compound 6 can be recovered by triturating the residue
with hot absolute ethanol. This procedure yielded only 0.35 g (60%)
of pure compound but no further purification was required.
1
C126H114 (1628.25): calcd. C 92.9, H 7.1; found C: 92.4, H 7.7. H
NMR (CD2Cl2): δ ϭ 8.87Ϫ8.83 (m, 4 H), 8.37 (d, J ϭ 8 Hz, 2 H),
8.87 (d, Jϭ 7.5 Hz, 2 H), 7.78Ϫ7.72 (m, 12 H), 7.60Ϫ7.58 (m, 8
H), 7.53 (dd, J1 ϭ J2 ϭ 7 Hz, 2 H), 7.37 (dd, J1 ϭ J2 ϭ 7.5 Hz,
4 H), 6.9Ϫ6.83 (m, 8 H), 1.52 (br. s, 72 H) ppm. 13C NMR
(CDCl3): δ ϭ 152.0, 137.7, 137.5, 137.2, 137.2, 136.6, 135.4, 135.3,
Compound 7: With toluene as solvent, the intermediate 7 was isol-
ated by precipitation with light petroleum ether in 46% yield. 133.2, 132.5, 132.2, 129.8, 129.5, 128.7, 127.7, 127.3, 127.0, 126.4,
C54H55Br (783.92): calcd. C 82.74; H 7.07; found C 82.81, H 7.09.
124.8, 123.8, 123.4, 122.7, 121.2, 119.9, 101.2, 91.9, 77.5, 76.9, 76.4,
1H NMR (CDCl3): δ ϭ 7.67 (d, J ϭ 8.2 Hz, 1 H), 7.58Ϫ7.52 (m,
35.2, 31.9 ppm. MS (DCI, NH3): m/z ϭ 1628 [MHϩ].
4188
Eur. J. Org. Chem. 2002, 4185Ϫ4189

Synthesis of Polyaromatic Hydrocarbons with a Central Rotor
FULL PAPER
Compound 2: An oven-dried Schlenk flask was filled with argon
and charged with 6 (400 mg, 0.51 mmol), 1,4-benzenediboronic
acid bis(neopentylglycol) cyclic ester (72 mg, 0.24 mmol), CsF
(155 mg, 1.02 mmol), and Pd2(dba)3 (7 mg, 0.008 mmol). After a
few vacuum/argon cycles, THF (25 mL) and a 0.01  solution of
tBu3P in THF (1.8 mL, 0.018 mmol) were added through a rubber
septum. After refluxing for 48 h, the mixture was allowed to cool
to room temperature, then diluted with THF (25 mL), filtered
through a short pad of silica gel, and concentrated under vacuum.
The deep yellow residue was purified by flash chromatography
[light petroleum ether/dichloromethane (9:1)], to provide lander 2
(145 mg, 41%) as a yellow solid. C114H110 (1480.1): calcd. C 92.5,
Acknowledgments
This work was supported by the CNRS, the European Community
FET-NID project BUN (Bottom-Up Nanomachines) IST-1999-
11565 and the TMR Atomic/molecular Manipulation FMRX-
CT97-0146.
[1]
C. Joachim, J. K. Gimzewski, A. Aviram, Nature 2000, 408,
541Ϫ548.
[2]
J. K. Gimzewski, C. Joachim, Science 1999, 283, 1683Ϫ1688.
[3]
C. Joachim, J. K. Gimzewski, Chem. Phys. Lett. 1997, 265,
353Ϫ357.
[4]
D. M. Eigler, E. K. Schweizer, Nature 1990, 344, 524Ϫ526.
F. Moresco, G. Meyer, K. H. Rieder, H. Tang, A. Gourdon, C.
1
H 7.49; found C 91.9, H 8.1. H NMR (CDCl3): δ ϭ 7.92 (d, J ϭ
[5]
8.2 Hz, 2 H), 7.71 and 7.69Ϫ7.67 (d, m, J ϭ 8.2 Hz, 8 H), 7.64 (s,
4 H), 7.58 and 7.56 (2 d, J1 ϭ J2 ϭ 1.8 Hz, 8 H), 7.41Ϫ7.30 (m,
8 H), 6.86Ϫ6.78 (m, 8 H), 1.42 (br. s, 72 H) ppm. 13C NMR
(CDCl3): δ ϭ 152.0, 139.3, 138.8, 138.0, 137.1, 136.9, 136.7, 136.2,
135.2, 135.1, 133.6, 133.3, 130.2, 129.6, 128.6, 127.9, 127.7, 126.3,
125.2, 123.5, 123.2, 123.1, 122.1, 35.2, 31.6 ppm. MS (DCI, NH3):
m/z ϭ 1479 [MHϩ], 1497 [MNH4ϩ].
Joachim, Phys. Rev. Lett. 2001, 87, 8302Ϫ8306.
[6]
H. J. Lee, W. Ho, Science 1999, 286, 1719Ϫ1722.
[7]
S.-W. Hla, L. Bartels, G. Meyer, K.-H. Rieder, Phys. Rev. Lett.
2000, 85, 2777Ϫ2780.
[8]
A. Gourdon, Eur. J. Org. Chem. 1998, 2797Ϫ2801.
[9]
V. J. Langlais, R. R. Schlittler, H. Tang, A. Gourdon, C.
Joachim, J. K. Gimzewski, Phys. Rev. Lett. 1999, 83,
2809Ϫ2812.
[10]
Compound 3: An oven-dried Schlenk flask was filled with argon
and charged with 6 (400 mg, 0.51 mmol), 4,4Ј-biphenyldiboronic
acid bis(neopentylglycol) cyclic ester (90 mg, 0.24 mmol), CsF
(155 mg, 1.02 mmol), and Pd2(dba)3 (7 mg, 0.008 mmol). After a
few vacuum/argon cycles, THF (25 mL) and a 0.01  solution of
tBu3P in THF (1.8 mL, 0.018 mmol) were added through a rubber
septum. After refluxing for 48 h, the mixture was allowed to cool
to room temperature, then diluted with THF (25 mL), filtered
through a short pad of silica gel, and concentrated under vacuum.
The deep yellow residue was purified by flash chromatography
[light petroleum ether/dichloromethane (9:1)], to provide lander 3
(170 mg, 46%) as a yellow solid. C120H114 (1556.2): calcd. C 92.6,
F. Rosei, M. Schunack, P. Jiang, A. Gourdon, E. Laegsgaard,
I. Stensgaard, C. Joachim, F. Besenbacher, Science 2002, 296,
382Ϫ331.
[11]
F. Moresco, G. Meyer, K. H. Rieder, H. Tang, A. Gourdon, C.
Joachim, Phys. Rev. Lett. 2001, 86, 672Ϫ675.
T. Zambelli, H. Tang, J. Lagoute, S. Gauthier, A. Gourdon, C.
[12]
Joachim, Chem. Phys. Lett. 2001, 348, 1Ϫ6.
[13]
O. Possel, A. M. van Leusen, Tetrahedron 1977, 48,
4229Ϫ4232.
[14]
G. Rule, S. B. Thompson, J. Chem. Soc. 1937, 1761Ϫ1763.
[15]
G. T. Crisp, Y.-L. Jiang, Synth. Commun. 1998, 28, 2571Ϫ2576.
[16]
M. Alami, F. Ferri, G. Linstrumelle, Tetrahedron Lett. 1993,
34, 6403Ϫ6406.
[17]
1
A. F. Littke, G. C. Fu, Angew. Chem. Int. Ed. 1998, 37,
3387Ϫ3388.
A. F. Littke, C. Dai, G. C. Fu, J. Am. Chem. Soc. 2000, 122,
4020Ϫ4028.
S. L. Buchwald, J. M. Fox, Strem Chem. 2000, 18(1), 1Ϫ12.
B. F. Duerr, Y.-S. Chung, A. W. Czarnik, J. Org. Chem. 1988,
H 7.4; found C 92.1, H 7.8. H NMR (CDCl3): δ ϭ 7.90 (d, J ϭ
8.3 Hz, 2 H), 7.78Ϫ7.63 (m, 16 H), 7.58 and 7.57 (2 d, J1 ϭ J2 ϭ
1.8 Hz, 8 H), 7.40Ϫ7.31 (m, 8 H), 6.87Ϫ6.79 (m, 8 H), 1.43 (br. s,
72 H) ppm. 13C NMR (CDCl3): δ ϭ 151.9, 139.5, 139.2, 139.0,
138.0, 137.0, 136.7, 135.1, 135.0, 133.6, 133.2, 130.7, 129.6, 128.4,
127.9, 127.6, 126.9, 126.2, 125.1, 123.5, 123.1, 121.1, 116.7, 35.1,
31.6 ppm. MS (DCI, NH3): m/z ϭ 1556 [MHϩ ϩ 1], 1573
[MNH4ϩ].
[18]
[19]
[20]
53, 2120Ϫ2122.
Received June 19, 2002
[O02342]
Eur. J. Org. Chem. 2002, 4185Ϫ4189
4189