Directed synthesis of symmetric and dissymmetric molecular motors built around a ruthenium cyclopentadienyl tris(indazolyl)borate complex

Article abstract of DOI:10.1016/j.tet.2008.08.071

This article focuses on the synthesis of a family of rotary molecular motors based on a penta-substituted cyclopentadienyl tris(indazolyl)borate ruthenium(II) complex. In order to demonstrate a movement of rotation in this family of molecular motors, diss

Full text of DOI:10.1016/j.tet.2008.08.071

Tetrahedron 64 (2008) 11462–11468
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Directed synthesis of symmetric and dissymmetric molecular motors built around
a ruthenium cyclopentadienyl tris(indazolyl)borate complex
a
a,b,
*
Guillaume Vives , Gw e´ na e¨ l Rapenne
a
NanoSciences Group, CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, F-31055 Toulouse Cedex 4, France
Universit e´ de Toulouse, UPS, 118 route de Narbonne, 31062 Toulouse, France
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 May 2008
Received in revised form 12 August 2008
Accepted 20 August 2008
Available online 27 August 2008
This article focuses on the synthesis of a family of rotary molecular motors based on a penta-substituted
cyclopentadienyl tris(indazolyl)borate ruthenium(II) complex. In order to demonstrate a movement of
rotation in this family of molecular motors, dissymmetric derivatives with one ferrocene missing have
also been synthesized. The molecules have been prepared with ester and thioether-functionalized
tris(indazolyl)borate ligands in view of studying them as single molecules on various surfaces by STM or
AFM techniques.
Keywords:
Ó 2008 Elsevier Ltd. All rights reserved.
Cyclopentadienone
Cyclopentadiene ligand
Dissymmetrized ligand
Ruthenium
Molecular motor
1. Introduction
anchored on a surface (i.e., a stator) and a substituted pentaphe-
nylcyclopentadienyl (Cp) ligand with five arms terminated by
9
A current trend in the physical and biological sciences is the
miniaturization of machinery from the macroscopic to the micro-
scopic world. To achieve this goal two complementary strategies
electroactive groups (i.e., a rotor). The functionalized tripodal li-
gands were designed to have three anchoring groups pointing in
the opposite direction of the coordination site in order not to in-
1
10
have been developed, giving birth to nanosciences. The first one is
the ‘top-down’ approach, which consists in the miniaturization of
existing objects following micro-scale technologies. Micro-scale
machines are the ultra-miniaturized versions of machines of our
everyday life. However, this approach is reaching some physical
limits due to the incompatibility of such technology with the 1–10
nm scale. The opposite approach, known as the ‘bottom-up’ strat-
egy, starts from atoms and molecules and follows a monumentali-
terfere sterically with it. Each functional group is connected at the
6-position of indazole, which should be the optimal orientation for
anchoring on a surface. The ester function has been found to
11
strongly interact with oxide surfaces,
being spontaneously
deprotected to the acid during the deposition process. In order to
Fe
2
zation strategy consisting in the association of different modular
functional units through the formation of covalent bonds within
only one molecule, which provides sufficient resources for the
Fe
Fe
3
-4
molecule to be a machine.
Among theses machines, molecular
rotary motors represent a particular challenge for the control of
5
a unidirectional movement.
Fe
Ru
Fe
6
In our laboratory, we have designed an electrically fuelled
molecular rotary motor aimed at being studied as a single molecule
by near-field microscopic techniques. This family of molecular
N
N
N
N
N
N
7
motors is based on a piano stool ruthenium complex (Fig. 1) with
a tripodal hydrotris(indazolyl) borate ligand functionalized to be
B
H
8
O
O
O
O
O
O
*
Corresponding author. Tel.: þ33 (0) 5 62 25 78 41; fax: þ33 (0) 5 62 25 79 99.
E-mail address: rapenne@cemes.fr (G. Rapenne).
Figure 1. Molecular motor functionalized for oxide surface deposition.
0
040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.08.071

G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
11463
interact with a metallic surface, the thioether function was chosen
to alleviate the problem encountered with oxidatively unstable
thiols and is known to interact strongly with a gold surface.
and study of physico-chemical properties of various molecules.17
These techniques allow the visualization and manipulation of only
12
18
one molecule and therefore the electrical and mechanical prop-
19
The motor is constituted of electron rich aromatic building
blocks to obtain a structure with maximum rigidity and with
a minimum of degrees of freedom. This rigidity is crucial in view of
recovering most of the work produced by the rotation of the upper
Cp ligand. The principle of this motor is to deposit the molecule
between two electrodes of a nanojunction and to control the ro-
erties of a single molecule deposited on a surface can be in-
vestigated. For this kind of studies, STM is often preferred to AFM
due to its higher resolution and the possibility to simulate the
images. However, conducting or semi-conducting surfaces are re-
quired for STM imaging. Recently, a tris(indazolyl)borate ligand
functionalized by thioether groups has been described to anchor
organometallic complexes onto metallic surfaces suitable for STM
13
tation by the flow of electrons.
10
In this kind of system, a crucial problem lies in a practical way to
evidence the rotation. Due to the high symmetry of the molecule,
imaging. We have subsequently designed a molecular motor
suitable for metallic surface deposition (1) by incorporating this
functionalized scorpionate ligand. The synthetic route (Scheme 1)
is based on a modular strategy using a quintuple palladium cata-
lyzed coupling reaction between the versatile pentabrominated
ruthenium complex (3) and ethynylferrocene.
ꢀ
two images obtained after a 72 rotation are indistinguishable with
5
a C -symmetric rotor such as a Cp carrying five identical sub-
stituents. However, this issue can be partly addressed by using
compounds of lower symmetry or tagged compounds.1 For that
purpose, we designed a dissymmetrized rotor in which one ferro-
cene electroactive group is missing. Lowering the symmetry of the
molecule should help to prove a movement and monitor the rota-
tion, the missing ferrocene acting as a probe for the position of the
rotor.
4
The ruthenium complex 3 was prepared by heating under mi-
5
crowave irradiation in a sealed tube bromo
h
-1,2,3,4,5-penta-(p-
10
bromophenyl)cyclopentadienyl dicarbonyl ruthenium(II) (2) with
potassium hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate
in a mixture of DMF and acetonitrile. After purification by column
chromatography, 3 was obtained in a 24% yield. The coupling be-
tween an alkyne and an aryl bromide is in general achieved under
The initial design involves a motor deposited between two
metallic nanoelectrodes on an insulating surface. To reach this goal,
we have recently reported the synthesis of a molecular motor with
21
3 4
Sonogashira conditions, i.e., using catalytic CuI and Pd(PPh ) .
15
ester-functionalized tris(indazolyl)borate stators designed to be
deposited on insulating oxide surfaces used in molecular scale
Non-Contact Atomic Force Microscope (NC-AFM) experiments.
However, preliminary experiments using Scanning Tunnelling
Microscopy (STM) on a conducting surface should be easier to
interpret and thus very useful to understand the behaviour of the
molecule.16 Moreover, for a molecule deposited near an atomic step
of the surface, the STM tip and the surface could also act as the two
electrodes of a nanojunction and an electro-induced rotation might
be observed. Thus the synthesis of a stator functionalized for the
deposition onto metallic surfaces used in STM experiments is also
required.
However, the five bromines in 3 are strongly deactivated towards
the oxidative addition step on the palladium catalyst by the con-
nection to a formal anionic entity (Cp). Nevertheless, Negishi cou-
2
2
pling conditions using a solution of [(ferrocenyl)ethynyl]zinc
chloride and Pd(PPh in refluxing THF were successful. Com-
3 4
)
pound 1 was isolated after purification by column chromatography
1
in 42% yield corresponding to 84% by coupling reaction. H NMR
0
0
spectroscopy clearly showed an AA BB pattern for the phenyl
groups attached to the central Cp ring, the quadruplet and triplet
system of the ethyl groups of the thioeter and an integration of 45
protons for the ferrocene moieties. The presence of the five ferro-
cene units was also confirmed by MALDI-TOF spectrometry.
In this paper, we report the synthesis of symmetric and dis-
symmetric molecular motors functionalized for metallic surface
deposition. The dissymmetric analogue functionalized for oxide
surfaces is also reported.
2
.2. Dissymmetric Cp ligand synthesis
In order to monitor the rotation by near-field microscopy,
a dissymmetric rotor with only four electroactive groups could
be a promising candidate since the missing group could act as
a probe. A rational synthesis of a dissymmetrized pentaphe-
nylcyclopentadienyl ligand is thus needed. The coupling of
2
2
. Results and discussion
.1. Symmetric motor for STM experiments
4
equiv of ethynylferrocene with 1-bromo-1,2,3,4,5-p-bromophe-
In the last decade, the continuous improvement of near-field
microscopic techniques such as STM or AFM has led to the imaging
nylcyclopentadiene gives access to the statistical mixture of
penta-, tetra-, tri-, di- and mono-ferrocenyl compounds, which
Fe
Br
Br
Fe
Fe
Br
Br
Br
Br
a
b
Br
Br
Br
Ru
Br
Fe
Ru
Fe
Ru
OC
CO Br
N
N
N
N
N
N
N
N
N
N
N
N
B
H
B
H
SEt
EtS
EtS
SEt
EtS
EtS
2
3
1
ꢀ
Scheme 1. Reagents and conditions: (a) potassium hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate, microwave, DMF/CH
nyl]zinc chloride, Pd(PPh , THF, reflux, 24 h, 42%.
3
CN, 120 C, 10 min, 24%; (b) [(ferrocenyl)ethy-
3 4
)

11464
G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
O
Br
HO
Br
Br
Br2
X
a
Br
Br
4
6
Br2
Br
b
5
ꢀ
2
Scheme 2. Reagents and conditions: (a) 4-tert-butylphenyllithium, Et O, 2 h, 81%; (b) HBr, AcOH, 95 C, 2 h, 78%.
cannot be separated due to their similar polarities (only the
penta-substituted product can be separated since its high sym-
metry decreases its polarity and brings a good differentiation
with respect to the others). We therefore opted for a controlled
synthesis of the tetra-ferrocenyl derivative. The key feature of
our strategy is to block one position of the Cp ring during the
synthesis, in order to differentiate it from the other four
substituents.
our case, a methyl group was chosen as a convenient 1H NMR
probe.
The first step involves the condensation of 1,3-di(4-bromophe-
2
6
0
nyl)propan-2-one with 4,4 -dibromobenzil under basic condi-
tions, yielding the tetrabrominated cyclopentadienone 7 in 68%
yield after recrystallization. The p-tolyl substituent is then in-
troduced by a nucleophilic addition of the Grignard reagent p-tol-
27
ylmagnesium bromide. The functionalized cyclopentadienol 8 is
obtained after recrystallization in hexane in an 88% yield as a single
regioisomer. In the pentaphenylcyclopentadiene family, it is
In this objective, the first idea (Scheme 2) was a bromination of
the pentaphenyl-cyclopentadienol (4) in which one phenyl group
is para-substituted by a tert-butyl blocking group. Compound 4
was obtained by a nucleophilic addition of 4-tert-butylphe-
nyllithium on the pentaphenyl cyclopentadienone in an 81%
2
8
known that coordination is not possible via the classical cyclo-
pentadienide generated under basic conditions because of the
strong steric hindrance. The coordination of ruthenium to this type
of ligand can only take place if there is a bromine atom on the Cp
2
3
yield. The selective bromination in the para positions of the
2
9
pentaphenylcylopentadiene has been described with neat bro-
ring, following Manners’ methodology, which consists of the
oxidative addition of the carbon–bromine bond on the ruthenium
carbonyl cluster. For that purpose, the hydroxy group of 8 was
replaced by a bromine atom. After reaction with HBr in acetic acid,
the brominated Cp 9 was purified by column chromatography and
was obtained in 62% yield as a mixture of three regioisomers
(Fig. 2).
2
0
mine at room temperature. However, a selective bromination of
under these conditions could not be achieved and only a mixture
4
of polybrominated products was observed. Supposing that the
hydroxyl group could be responsible for these selectivity prob-
lems, it was substituted by a bromine using a mixture of hydro-
2
4
bromic acid and acetic acid to yield 5. Bromination attempts
with neat bromine or in solution in CCl with or without iron were
4
The three regioisomers of 9 are probably formed via an SN
1
0
unsuccessful. Compound 6 could not be obtained selectively in
a good yield.
mechanism since the SN
2
and SN
2
mechanisms would give rise
only to one or two regioisomers, respectively. Their proportion can
1
Nevertheless, this issue could be overcome following an
be quantified by H NMR, using the methyl group of the tolyl
alternative strategy by using
Grignard reagent on the tetrabrominated cyclopentadienone (7)
Scheme 3). This modular strategy could allow the introduction
of a large variety of substituents in a controlled manner. In
a
nucleophilic addition of
a
substituent as a probe. In the aliphatic region three singlets are
observed (Fig. 3, top), corresponding to the three regioisomers with
a 1.4:1.7:1.9 ratio, which is close to the statistical 1:2:2 mixture. The
formation of pentaarylcyclopentadienyl carbocations from the
2
5
(
Br
Br
O
+
O
HO
Br
Br
Br
Br
Br
Br
Br
a
b
c
O
O
Br
Br
Br
Br
Br
Br
Br
Br
7
8
9
ꢀ
ꢀ
Scheme 3. Reagents and conditions: (a) KOH, EtOH, reflux, 40 min, 68%; (b) 4-tolylmagnesium bromide, THF, 25 C, 2 h, 88%; (c) HBr, AcOH, 95 C, 2 h, 62%. Compound 9 was
obtained as a mixture of three regioisomers.

G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
11465
CH3
Br
Br
Br
Br
Br
Br
Br
Br
Br
CH3
Br
Br
Br
Br
Br
Br
CH3
Figure 2. The three regioisomers formed simultaneously during the synthesis of the brominated cyclopentadiene 9.
corresponding alcohols under acidic conditions has been studied in
3
0
þ
detail. It must be stated that the postulated Cp intermediate is
antiaromatic. The presence of this mixture of regioisomers is not
a problem since the next step, which consists in the aromatization
of the Cp ring through its coordination, leads to the same com-
pound for all three regioisomers.
2.3. Dissymmetric molecular motor for oxide surfaces
The dissymmetric Cp ligand 9 was subsequently coordinated to
synthesize a molecular motor functionalized for oxide surface
grafting and AFM studies. As shown in Scheme 4, coordination of
3
the three regioisomers of ligand 9 with Ru (CO)12 gave complex 10
with a 48% yield after purification by column chromatography. The
two carbonyl groups and the bromide ligand can be substituted by
the hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate tripodal li-
gand by heating under microwave irradiation in a sealed tube at
ꢀ
1
1
50 for 10 min. The ruthenium precursor of the molecular motor
Figure 3. Top: 1H NMR (CD
corresponding to the three regioisomers in the 2–3 ppm region and the complex
signals in the aromatic region. Bottom: 1H NMR (CD
Cl , 250 MHz) spectrum of ru-
thenium complex 12 with one singlet corresponding to the methyl group in the
–3 ppm region.
2
2
Cl , 250 MHz) spectrum of ligand 9 with the three singlets
1 was subsequently reacted using the Negishi cross-coupling
conditions
symmetrized molecule 12 was obtained in 49% yield, which cor-
responds to 84% yield per coupling reaction. The presence of the
2
2
with [(ferrocenyl)ethynyl]zinc chloride. The dis-
2
2
2
Fe
2
1
Fe
4
3
Br
Br
5
6
Br
Br
Ru
Fe
Ru
Fe
a
b
N
N
N
N
N
N
N
N
N
N
N
N
c
c
B
H
B
H
d
O
O
O
O
O
O
b
O
O
O
O
O
O
Br
Br
Br
Br
Br
11
12
a
Br
Br
Ru
Fe
Fe
Br
Br
OC
CO Br
10
Br
d
Br
9
Mixture of
three regioisomers
e
Fe
Br
Br
Fe
Ru
Ru
N
N
N
N
N
N
N
N
N
N
N
N
B
H
B
H
SEt
EtS
EtS
SEt
EtS
EtS
13
14
ꢀ
Scheme 4. Reagents and conditions: (a) Ru
3
(CO)12, toluene, 2 h, reflux, 48%; (b) potassium hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate, microwave, DMF/CH
3
CN, 150 C,
CN,
1
0 min, 30%; (c) [(ferrocenyl)ethynyl]zinc chloride, Pd(PPh
3
)
4
, THF, reflux, 24 h, 49%; (d) potassium hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate, microwave, DMF/CH
3
ꢀ
0
0
ꢀ
120 C, 10 min, 27%; (e) ferroceneboronic acid, Pd(OAc) , 2-(2 ,6 -dimethoxybiphenyl) dicyclohexylphosphine, K PO , toluene, 100 C, overnight, 52%.
2
3
4

11466
G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
1
ferrocenyl moieties was confirmed by H NMR spectroscopy with
an integration of 36 for the protons of the ferrocenyl groups and 3
diethylamine over KOH. All reactions were carried out using
standard Schlenk techniques under an argon atmosphere. Flash
column chromatography was carried out on silica gel 230–400
mesh from SDS. NMR spectra were recorded on Bruker AM 250
spectrometer, Avance 300 and Avance 500, and full assignments
were made using COSY, ROESY, HMBC and HMQC methods
when necessary. Chemical shifts are defined with respect to
TMS¼0 ppm for H and C NMR spectra and were measured
relative to residual solvent peaks. The following abbreviations
have been used to describe the signals: s for singlet; d for
doublet; t for triplet; td for triplet of doublets; q for quadruplet;
m for multiplet. The numbering scheme is given in Scheme 4
(molecule 11, vide supra). UV–vis spectra were recorded on
a Shimadzu UV-3100 spectrometer. FAB and DCI mass spec-
trometry was performed using a Nermag R10-10.
1
for the protons of the tolyl group. Moreover, the H NMR spectrum
0
0
also clearly showed three AA BB patterns for the phenyl protons of
the rotor with a 2:2:1 ratio. MALDI-TOF spectrometry also con-
firmed the presence of the four ferrocene units.
1
13
2
.4. Dissymmetric molecular motor for metallic surfaces
A dissymmetric motor specially designed for STM studies with
a shorter rotor has been synthesized using a Suzuki coupling re-
31
action between ferroceneboronic acid and 13 (Scheme 4). Biaryl
bonds being less flexible than alkynes, the rigidity of the arms
should also be increased. Moreover, this design allows to avoid
triple bonds, which have been shown to be very reactive on me-
tallic surfaces.32
The ruthenium precursor 10 was reacted with the hydrotris[6-
(
(ethylsulfanyl)methyl) indazol-1-yl]borate tripodal ligand by
4.2. Synthesis
ꢀ
heating under microwave irradiation in a sealed tube at 120 to
0
0
4.2.1. h
5-1,2,3,4,5-Penta-(4-(ferrocenylethynyl)phenyl)
cyclopentadienyl hydrotris[6-((ethylsulfanyl)
yield 13. The Buchwald universal catalyst (2-(2 ,6 -dimethoxy-
biphenyl)dicyclohexylphosphine in the presence of palladium ac-
etate), which has been reported to be a very efficient Suzuki
methyl)indazol-1-yl]borate ruthenium(II) (1)
3
3
In a two-necked flask, a
solution of h5-1,2,3,4,5-penta-
coupling catalyst for deactivated substrates was thus chosen for
the quadruple coupling step. Therefore, the ruthenium complex 13
was reacted in toluene with two times 20 equiv of ferroceneboronic
acid in the presence of palladium acetate (0.3 equiv) and the
Buchwald phosphine (0.6 equiv). After purification by column
chromatography, the product of quadruple coupling 14 was
obtained in a 52% yield (corresponding to 85% per coupling re-
action). The product was characterized by mass spectrometry and
(4-bromophenyl)cyclopentadienyl hydrotris[6-((ethylsulfanyl)
methyl)indazol-1-yl]borate ruthenium(II) (3) (50 mg, 0.032 mmol)
and Pd(PPh ) (19 mg, 0.5 equiv) in 6 mL of freshly distilled THF was
3 4
degassed. A freshly prepared solution of 0.2 M (ferrocenylethynyl)zinc
chloride (0.65 mmol, 20 equiv) was then added. The mixture was
heated under reflux for 24 h. Additional reactants were added
3 4
(19 mg of Pd(PPh ) and 0.65 mmol of (ferrocenylethynyl)zinc
1
H NMR with an integration of 45 for the protons of the ferrocenyl
chloride) and heating at reflux was maintained for another 24 h. The
crude reaction mixture was evaporated under vacuum. The product
was adsorbed on silica and purified by flash column chromatogra-
groups and 3 for the H
was also characterized by MALDI-TOF mass spectrometry.
a
protons of the tripodal ligand. Compound
phy (SiO
(30 mg, 42%).
52,200), 437 (9300); H NMR (500 MHz, CD
2
: cyclohexane/CH
2
Cl
)/nm 265 (195,000), 305 (152,300), 358
Cl (ppm) 7.93 (s, 3H,
), 7.37 (d,10H, J¼8.5 Hz,
), 7.04 (dd, 3H, J¼8.7, 1 Hz, H ), 4.44 (t,
2
0–50%) to give 1 as an orange solid
3
. Conclusion
l
max
(
3
) (CH Cl
2
2
1
(
2
2
) d
In summary, we have synthesized a molecular motor function-
H
H
a
), 7.90 (s, 3H, H
d
), 7.39 (d, 3H, J¼8.7 Hz, H
b
alized for metallic surface deposition and STM imaging (compound
). In order to monitor the rotation, a versatile strategy to obtain
o
), 7.18 (d, 10H, J¼8.5 Hz, H
m
c
1
10H, J¼1.8 Hz, subs Cp), 4.21 (t, 10H, J¼1.8 Hz, subs Cp), 4.20 (s, 25H,
Cp), 3.90 (s, 6H, CH CH ), 1.28 (t, 9H,
S), 2.45 (q, 6H, J¼7.4 Hz, CH
); C NMR (126 MHz, CD Cl (ppm) 143.64, 140.39,
a dissymmetrized cyclopentadienyl ligand has been developed.
This ligand has been incorporated in the family of electron-fuelled
molecular rotary motors by coordination to a ruthenium tri-
s(indazolyl)borate complex to act as a dissymmetric rotor. Scanning
probe microscopic studies are underway, on oxide surfaces for the
ester-functionalized dissymetrized ruthenium complex (com-
pound 12) and metallic surfaces for the thioether-functionalized
dissymetrized ruthenium complex (compound 14) to prove the
rotation of the molecule. We are hoping to use the rotor of lower
symmetry for real-time imaging of the rotation.
2
2
3
13
J¼7.1 Hz, CH
3
2
2
) d
137.56, 133.56, 133.15, 130.19, 122.95, 122.17, 122.10, 120.03, 110.95,
89.34, 87.68, 85.26, 71.37, 69.93, 68.94, 64.95, 36.44, 25.23,14.34; MS
þ
(MALDI-TOF) m/z 2172.1 ([M ], 100%); High resolution LSI m/z
þ
2173.3055 ([MþH] , 100%, calculated for C125
5 6 3
H100BFe N RuS :
2173.3117).
4.2.2.
h
5-1,2,3,4,5-Penta-(4-bromophenyl)cyclopentadienyl
hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate
ruthenium(II) (3)
4
4
. Experimental section
.1. General
Bromo
h
5-1,2,3,4,5-penta-(4-bromophenyl)cyclopentadienyl
dicarbonyl ruthenium(II) (55 mg, 0.05 mmol, 1 equiv) and
potassium hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate
62 mg, 0.1 mmol, 2 equiv) were heated in a sealed tube at 100 C
ꢀ
(
All commercially available chemicals were of reagent grade and
were used without further purification. 4,4 -Dibromobenzil and
ethynylferrocene were purchased from Aldrich. Ruthenium car-
under microwave irradiation for 10 min in 2 mL of acetonitrile. The
crude reaction mixture was evaporated under vacuum. The product
was adsorbed on silica and purified by column chromatography
0
5
bonyl was purchased from Strem. Bromo
h
-1,2,3,4,5-penta-(4-
(SiO
24%).
2
, cyclohexane/CH
2
Cl
)/nm 295 (280,700), 312 (251,000), 397
Cl (ppm) 7.92 (s, 3H, H ), 7.83
), 7.39 (dd, 3H, J¼8.3, 0.6 Hz, H ), 7.27 (d, 10H,
), 7.23 (d, 10H, J¼8.9 Hz, H ), 7.08 (dd, 3H, J¼8.3, 1.3 Hz,
), 3.93 (s, 3H, CH ), 1.31 (t, 9H,
SEt), 2.50 (q, 6H, J¼7.4 Hz, CH
); C NMR (126 MHz, CD Cl (ppm) 143.63, 140.23,
2
40%) to give 3 as a yellow solid (20 mg,
2
0
bromophenyl)cyclopentadienyl dicarbonyl ruthenium(II) (2),
hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate,
hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate, 1-(4-tert-
butylphenyl)-2,3,4,5-tetraphenylcyclopentadien-1-ol(4), 1-bromo-
-(4-tert-butylphenyl)-2,3,4,5-tetraphenyl cyclopentadiene (5)
and 1,3-di(4-bromophenyl)propan-2-one were prepared accord-
ing to the literature procedures. Toluene was dried and distilled
l
max
1
2 2
(3) (CH Cl
10
potassium
(32,600); H NMR (500 MHz, CD
2
2
)
d
d
10
(d, 3H, J¼0.7 Hz, H
a
b
2
3
J¼8.9 Hz, H
o
m
2
4
1
H
c
2
2
2
6
13
J¼7.4 Hz, CH
3
2
2
) d
137.78, 135.14, 132.13, 130.65, 122.31, 122.00, 121.87, 120.02, 110.92,
þ
over CaH
2
,
THF over sodium with benzophenone and
87.06, 36.42, 25.27, 14.33; MS (DCI/NH
3
) m/z 1529.0 ([M ], 100%);

G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
11467
þ
High resolution LSI m/z 1528.8779 ([MþH] , 100%, calculated for
for 2 h in 15 mL of freshly distilled toluene. The solution was ini-
tially yellow turns rapidly to dark green and then to cherry red. The
crude reaction mixture was evaporated under vacuum. The crude
65 5 6 3
C H55BBr N RuS : 1528.8704).
4
.2.3. Tetra(4-bromophenyl)cyclopentadienone (7)
A solution of potassium hydroxide (160 mg, 2.8 mmol, 1 equiv)
product was purified by column chromatography (SiO
ane/CH Cl 0–20%) to give 10 as a yellow solid (400 mg, 48%). H
NMR (300 MHz, CD Cl (ppm) 7.29 (m, 8H, H , H ), 6.97 (d, 2H,
J¼8 Hz, H ), 6.92 (m, 10H, H , H , H ), 2.29 (s, 3H, CH
(76 MHz, CD Cl (ppm) 196.06, 139.33, 133.88, 133.86, 132.05,
2
, cyclohex-
1
2
2
in absolute ethanol (1.6 mL) was added to a refluxing solution of
4
mophenyl)propan-2-one (1.04 g, 2.8 mmol, 1 equiv) in absolute
2
2
)
d
3
5
0
13
,4 -dibromobenzil (1.04 g, 2.8 mmol, 1 equiv) and 1,3 di(4-bro-
1
2
4
6
3
); C NMR
2
2
) d
ethanol (4 mL). After 40 min at reflux, the mixture was cooled to
131.44, 131.34, 128.99, 128.66, 128.20, 125.48, 123.24, 123.06, 107.24,
ꢀ
ꢁ
0
C. The precipitate was filtered and washed with ethanol to give 7
105.76, 104.86, 21.04; MS (DCI/NH
3
) m/z 972 [MþNH
3
ꢁ2CO] , 956
1
ꢁ
ꢁ1
as a purple solid (1.5 g, 68%). H NMR (250 MHz, CD
.34 (m, 8H), 7.09 (d, 4H, J¼8.5 Hz), 6.80 (d, 4H, J¼8.5 Hz); C NMR
63 MHz, CDCl (ppm) 194.96, 135.47, 131.77, 131.57, 131.15,
30.77, 128.94, 123.89, 123.59, 122.45; MS (DCI/NH ) m/z 701
] . Elemental analysis: calcd for C29 O:
C 49.7, H 2.3; found: C 49.4, H 2.2.
2
Cl
2
)
d
(ppm)
[Mꢁ2CO] ; IR:
n
C]O 2007 (s) and 2048 (s) cm
.
13
7
(
3
)
d
4.2.7.
hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate ruthenium(II) (11)
h
5-1-(4-Tolyl)-2,3,4,5-tetra(4-bromophenyl)cyclopentadienyl
1
3
þ
þ
5
[MþH] , 718 [MþNH
4
H16Br
4
Bromo h -1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl)cyclopenta-
dienyl dicarbonyl ruthenium(II) (10) (50 mg, 0.05 mmol, 1 equiv)
and potassium hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate
ꢀ
4.2.4. 1-(4-Tolyl)-2,3,4,5-tetra(4-bromophenyl)
(61 mg, 0.1 mmol, 2 equiv) were heated in a sealed tube at 150 C
cyclopentadien-1-ol (8)
under microwave irradiation for 10 min in a mixture of 2 mL of
acetonitrile and 1 mL of DMF. The crude reaction mixture was
evaporated under vacuum. The product was adsorbed on silica and
In a Schlenk tube under argon, a solution of p-tolylmagnesium
bromide 1 M in THF (2 mL, 2 mmol, 2 equiv) was added dropwise at
room temperature to a suspension of tetra(4-bromophenyl)cyclo-
pentadienone (7) (700 mg, 1 mmol, 1 equiv) in 10 mL of THF. The
solutionwas stirred2 hat room temperatureand the colourchanged
from purple to yellow. The solution was hydrolyzed by adding water
and 1 M HCl. After washing with water, extractionwith diethyl oxide
and dryingover magnesium sulfate, the solvent was evaporated. The
purified by column chromatography (SiO
2
, dichloromethane) to
give 11 as a yellow solid (22 mg, 30%). H NMR (500 MHz, CD Cl
(ppm) 8.76 (s, 3H, H ), 7.96 (s, 3H, H
), 7.68 (d, 3H, J¼8.5 Hz, H
7.44 (d, 3H, J¼8.5 Hz, H ), 7.21 (br s, 18H, H , H3-6), 6.89 (d, 2H,
J¼8.0 Hz, H ), 4.47 (q, 6H, J¼7.1 Hz, CH ), 2.23 (s, 3H, PhCH ), 1.48 (t,
9H, J¼7.1 Hz, CH ); C NMR (126 MHz, CD Cl (ppm) 166.77,
1
2
2
)
d
d
a
c
),
b
1
2
2
3
13
3
2
2
) d
crude product was recrystallized in hexane to afford 8 as a white
143.07, 140.73, 137.98, 135.15, 135.07, 133.26, 132.26, 131.94, 130.73,
130.67, 129.02, 128.89, 128.31, 125.25, 121.99, 121.87, 121.05, 119.73,
1
solid (700 mg, 88%). H NMR (250 MHz, CD
2
Cl
2
)
d
(ppm) 7.45 (d, 2H,
J¼8.1 Hz), 7.36 (d, 4H, J¼8.5 Hz), 7.22 (d, 4H, J¼8.6 Hz), 7.15 (d, 2H,
113.85, 90.17, 88.05, 87.28, 61.29, 20.87, 14.24; MS (DCI/NH
3
) m/z
] , 1457 [MþH] ; MS (MALDI-TOF) m/z 1451.9678
51BBr Ru: 1451.9740).
þ
þ
J¼8.1 Hz), 6.94 (d, 4H, J¼8.6 Hz), 6.90 (d, 4H, J¼8.5 Hz), 2.59 (s, 1H,
1474 [MþNH
4
1
3
þ
OH), 2.33 (s, 3H, CH
3
); C NMR (100 MHz, CDCl
3
)
d
(ppm) 134.01,
([M ], 100%, calculated for C66
H
4 6 6
N O
1
33.30, 132.41, 132.28, 132.09, 131.91, 131.89, 131.66, 131.37, 131.13,
131.05, 130.22, 130.04, 129.23, 123.66, 21.74; MS (DCI/NH
3
) m/z 793
] . Elemental analysis: calcd
4.2.8. h
5-1-(4-Tolyl)-2,3,4,5-tetra(4-(ferrocenylethynyl)
phenyl)cyclopentadienyl hydrotris[6-(ethoxy
carbonyl)indazol-1-yl]borate ruthenium(II) (12)
In a two-necked flask was placed a solution of 11 (30 mg,
þ
þ
þ
[
MþH] , 810 [MþNH
4
] , 827 [MþN
2
H
7
for C36
H24Br
4
O: C 54.3, H 3.0; found: C 54.6, H 3.1.
4
.2.5. 1-Bromo-1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl)
cyclopentadiene (mixture of isomers) (9)
-(4-Tolyl)-2,3,4,5-tetra(4-bromophenyl)cyclopentadien-1-ol
0.02 mmol) and Pd(PPh
freshly distilled THF.
(ferrocenylethynyl)zinc chloride (0.40 mmol, 20 equiv) was then
added. The mixture was heated under reflux for 24 h. Additional
3
)
4
(12 mg, 0.5 equiv) in 4 mL of
A
freshly prepared solution of 0.2 M
1
(8) (200 mg, 0.25 mmol, 1 equiv) was suspended in glacial acetic
ꢀ
acid (4 mL). The solution was heated under argon to 60 C and
a solution of 48% HBr (0.4 mL) in glacial acetic acid (1.4 mL) was
added dropwise. After addition, the solution was stirred at 95 C for
3 4
reactants were added (12 mg Pd(PPh ) and 0.40 mmol of
(ferrocenylethynyl)zinc chloride) and heating at reflux was main-
tained for another 24 h. The crude reaction mixture was evaporated
under vacuum. The product was adsorbed on silica and purified by
ꢀ
2
h. After cooling down, water was added to precipitate the prod-
uct, and it was filtered and washed with water. The crude product
was purified by column chromatography (SiO : cyclohexane/
CH Cl 0–10%) to give 9 as a yellow solid (135 mg, 62%) as mixture
of isomers. ) (CH Cl )/nm 260 (33,100), 285 (36,100), 373
3600); H NMR (250 MHz, CD Cl (ppm) 7.4–6.8 (m, 20H), 2.32
s, 0.84H, regioisomer 1CH ), 2.29 (s, 1.14H, regioisomer 2CH ), 2.24
s, 1.02H, regioisomer 3CH (ppm)
49.23, 148.26, 147.63, 147.38, 146.69, 142.57, 141.80, 141.35, 140.72,
40.19, 138.52, 138.02, 137.88, 134.55, 134.52, 133.31, 133.13, 133.03,
33.00, 132.90, 132.78, 132.66, 132.05, 131.98, 131.86, 131.74, 131.70,
31.66, 131.64, 131.41, 131.28, 131.22, 131.05, 130.93, 130.70, 130.19,
29.75, 129.47, 129.36, 129.30, 128.96, 128.59, 127.31, 122.32, 122.22,
22.03, 121.99, 121.92, 121.90, 121.82, 121.66, 21.08, 20.98, 20.85; MS
flash column chromatography (SiO
solid (20 mg, 49%). ) (CH Cl
365 (42,600); H NMR (500 MHz, CD
8.07 (s, 3H, H
), 7.67 (d, 3H, J¼8.5 Hz, H
7.36 (m, 8H, H , H
), 7.27 (d, 2H, J¼8.2 Hz, H
6.91 (d, 2H, J¼8.2 Hz, H ), 4.47 (q, 6H, J¼7.1 Hz, CH
J¼1.8 Hz, subs Cp), 4.21 (m, 8H, subs Cp), 4.20 (s, 10H, Cp), 4.19 (s,
2
: CH
2 2
Cl ) to give 12 as an orange
2
l
max
(3
2
2
)/nm 262 (97,000), 308 (85,500),
1
2
2
2
Cl
), 7.48 (d, 3H, J¼8.5 Hz, H
), 7.18 (m, 8H, H , H
2
)
d
(ppm) 8.79 (s, 3H, H
d
),
b
),
6
),
l
max
(3
2
2
a
c
1
(
(
(
1
1
1
1
1
1
2
2
)
d
3
5
1
4
3
3
2
2
), 4.44 (t, 8H,
13
3
2 2
); C NMR (76 MHz, CD Cl ) d
1
3
10H, Cp), 2.25 (s, 3H, CH
3
), 1.48 (t, 9H, J¼7.1 Hz, CH
3
); C NMR
(126 MHz, CD Cl (ppm) 166.86, 143.09, 140.87, 137.75, 133.56,
2
2
) d
133.49, 133.39,132.99, 132.82, 130.27, 130.22, 129.48, 128.88, 128.21,
125.36, 123.13, 123.03, 120.97, 119.75, 113.85, 89.82, 89.52, 89.46,
88.58, 88.29, 85.18, 71.38, 70.66, 69.93, 68.98, 64.87, 61.27, 22.71,
þ
þ
14.25; MS (MALDI/TOF) m/z 1972 [M] ; HR-FAB –MS (m-NBA) m/z
ꢁ
þ
(
(
DCI/NH
MþH , calculated for C36
3
) m/z 856 [M] ; HR-FABMS (m-NBA) m/z 849.7654
1972.4070 (M , calculated for C114
4
H87BFe N
6
O
6
Ru: 1972.3221).
þ
H23Br
5
: 849.7717).
4
.2.9. h
5-1-(4-Tolyl)-2,3,4,5-tetra(4-bromophenyl)cyclopentadienyl
4.2.6. Bromo
h
5-1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl)
hydrotris[6-((ethylsulfanyl)methyl)indazol-1-yl]borate
cyclopentadienyl dicarbonyl ruthenium(II) (10)
Ruthenium carbonyl (175 mg, 0.27 mmol, 1 equiv) and 1-
bromo-1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl) cyclopentadiene
ruthenium(II) (13)
Bromo
dienyl dicarbonyl ruthenium(II) (10) (125 mg, 0.12 mmol, 1 equiv)
and potassium hydrotris[6-((ethylsulfanyl)methyl)indazol-1-
h
5-1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl)cyclopenta-
(9) (700 mg, 0.82 mmol, 3 equiv) were heated under argon at reflux

11468
G. Vives, G. Rapenne / Tetrahedron 64 (2008) 11462–11468
yl]borate (154 mg, 0.24 mmol, 2 equiv) were heated in a sealed
tube at 120 C under microwave irradiation for 10 min in a mixture
of 2 mL of acetonitrile and 1 mL of DMF. The crude reaction mixture
was evaporated under vacuum. The product was adsorbed on silica
2. Feynman, R. P. The Pleasure of Finding Things Out; Perseus Books: Cambridge,
Massachusetts, 1999.
ꢀ
3
. A special issue on ‘‘Molecular Machines’’ has been pubished in Acc. Chem. Res.
001, 34.
4. (a) Kottas, G. S.; Clarke, L. I.; Horinek, D.; Michl, J. Chem. Rev. 2005, 105, 1281–
376; (b) Leigh, D. A.; Zerbetto, F.; Kay, E. R. Angew. Chem., Int. Ed. 2007, 46, 72–
91; (c) Shirai, Y.; Morin, J. F.; Sasaki, T.; Guerrero, J. M.; Tour, J. M. Chem. Soc.
2
1
1
2
and purified by column chromatography (SiO , cyclohexane/
dichloromethane 50:50) to give 13 as a yellow solid (50 mg, 27%).
Rev. 2006, 35, 1043–1055.
1
H NMR (300 MHz, CD
2
Cl
), 7.27–7.16 (m, 18H, H
), 6.87 (d, 2H, J¼8.0 Hz, H ), 3.90 (s, 6H, CH
CH ), 2.22 (s, 3H, PhCH
), 1.27 (t, 9H, J¼7.4 Hz,
); C NMR (76 MHz, CD Cl (ppm) 143.71, 140.37, 137.74,
2
)
d
(ppm) 7.88 (s, 3H, H
, H3–6), 7.03 (d, 3H,
S), 2.46 (q,
d
), 7.81 (s, 3H, H
a
),
5. (a) Horinek, D.; Michl, J. J. Am. Chem. Soc. 2003, 125, 11900–11910; (b) Ikeda,
M.; Takeuchi, M.; Shinkai, S.; Tani, F.; Naruta, Y.; Sakamoto, S.; Yamaguchi, K.
Chem.dEur. J. 2002, 8, 5541–5550; (c) Jian, H.; Tour, J. M. J. Org. Chem. 2003,
7
.33 (d, 3H, J¼8.4 Hz, H
b
1
J¼8.4 Hz, H
c
2
2
68, 5091–5103; (d) Kelly, T. R.; De Silva, H.; Silva, R. A. Nature 1999, 401,
6
H, J¼7.4 Hz, CH
2
3
3
150–152; (e) Kelly, T. R.; Silva, R. A.; De Silva, H.; Jasmin, S.; Zhao, Y. J. Am.
Chem. Soc. 2000, 122, 6935–6949; (f) Koumura, N.; Zijistra, R. W. J.; Van
Delden, R. A.; Harada, N.; Feringa, B. L. Nature 1999, 401, 152–155; (g) Leigh,
D. A.; Wong, J. K. Y.; Dehez, F.; Zerbetto, F. Nature 2003, 424, 174–179; (h)
Tashiro, K.; Konishi, K.; Aida, T. J. Am. Chem. Soc. 2000, 122, 7921–7926; (i)
Ter Wiel, M. K. J.; Van Delden, R. A.; Meetsma, A.; Feringa, B. L. J. Am. Chem.
Soc. 2003, 125, 15076–15086; (j) Browne, W. R.; Feringa, B. L. Nat. Nano-
technol. 2006, 1, 25–35.
1
3
CH
2
CH
3
2
2
) d
135.34,135.26, 133.45,132.77,132.50,130.65,130.58,129.44,128.24,
1
3
22.30, 122.10, 121.82, 121.70, 120.05, 111.00, 89.25, 87.16, 86.50,
þ
6.56, 30.25, 25.38, 20.94, 14.42; MS (FAB) m/z 1459 [MþH] ; MS
þ
(
MALDI-TOF) m/z 1457.9511 ([M ], 38%, calculated for
C
66
H57BBr
4
N
6
S
3
Ru: 1457.9677).
6. (a) Carella, A.; Rapenne, G.; Launay, J. P. New J. Chem. 2005, 29, 288–290; (b)
Vives, G.; Carella, A.; Sistach, S.; Launay, J.-P.; Rapenne, G. New J. Chem. 2006, 30,
1429–1438.
5-1-(4-Tolyl)-2,3,4,5-tetra(4-ferrocenylphenyl)
.2.10. h
4
7. Carella, A.; Coudret, C.; Guirado, G.; Rapenne, G.; Vives, G.; Launay, J.-P. Dalton
cyclopentadienyl hydrotris[6-((ethylsulfanyl)methyl)
indazol-1-yl]borate ruthenium(II) (14)
Trans. 2007, 177–186.
8. Rheingold, A. L.; Haggerty, B. S.; Yap, G. P. A.; Trofimenko, S. Inorg. Chem. 1997,
3
6, 5097–5103.
. Vives, G.; Carella, A.; Launay, J.-P.; Rapenne, G. Coord. Chem. Rev. 2008, 252,
451–1459.
In a Schlenk tube, 12 (30 mg, 0.020 mmol, 1 equiv), ferrocene-
boronic acid (94 mg, 0.40 mmol, 20 equiv), palladium acetate
9
1
0
0
(
2.3 mg, 10
hexylphosphine (8.5 mg, 20
43 mg, 0.20 mmol, 10 equiv) were placed under argon. Freshly
m
mol, 0.5 equiv), 2-(2 ,6 -dimethoxybiphenyl) dicyclo-
10. Carella, A.; Vives, G.; Cox, T.; Jaud, J.; Rapenne, G.; Launay, J.-P. Eur. J. Inorg.
Chem. 2006, 980–987.
m
mol, 1 equiv) and anhydrous K PO
3
4
1
1. (a) Kalyanasundaram, K.; Gr a¨ tzel, M. Coord. Chem. Rev. 1998, 177, 347–414; (b)
(
Galoppini, E.; Guo, W.; Qu, P.; Meyer, G. J. J. Am. Chem. Soc. 2001, 123, 4342–
4343; (c) Hoertz, P. G.; Carlisle, R. A.; Meyer, G. J.; Wang, D.; Piotrowiak, P.;
Galoppini, E. Nano Lett. 2003, 3, 325–330.
distilled toluene (2 ml) was added and the mixture was heated at
ꢀ
1
00 C overnight. After cooling down, additional ferroceneboronic
1
2. (a) Troughton, E. B.; Bain, C. D.; Whitesides, G. M.; Nuzo, R. G.; Allara, D. L.;
Porter, M. D. Langmuir 1988, 4, 365–385; (b) Noh, J.; Murase, T.; Nakajima, K.;
Lee, H.; Hara, M. J. Phys. Chem. B 2000, 104, 7411–7416; (c) Kittredge, K. W.;
Minton, M. A.; Fox, M. A.; Whitesell, J. K. Helv. Chim. Acta 2002, 85, 788–798; (d)
Furukawa, K.; Ebata, K.; Nakashima, H.; Kashimura, Y.; Torimitsu, K. Macro-
molecules 2003, 36, 9–11.
acid (94 mg, 0.40 mmol, 20 equiv), palladium acetate (2.3 mg,
0
0
1
0
m
mol, 0.5 equiv), 2-(2 ,6 -dimethoxybiphenyl) dicyclohexyl
phosphine (8.5 mg, 20 mol, 1 equiv) and anhydrous K PO (43 mg,
.20 mmol, 10 equiv) were added and the mixture was heated at
m
3
4
0
1
ꢀ
00 C overnight. The crude reaction mixture was evaporated un-
13. Rapenne, G. Org. Biomol. Chem. 2005, 3, 1165–1169.
der vacuum. The product was purified by column chromatography
14. (a) Gross, L.; Rieder, K. H.; Moresco, F.; Stojkovic, S.; Gourdon, A.; Joachim, C.
Nat. Mater. 2005, 4, 892–895; (b) Vives, G.; Rapenne, G. Tetrahedron Lett. 2006,
(
(
3
(
Al
20 mg, 52%).
59 (42,600), 436 (7400); H NMR (500 MHz, CD
s, 3H, H ), 7.81 (s, 3H, H ), 7.34 (m, 11H, H , H
J¼8.1 Hz, H ), 7.18 (m, 8H, H , H ), 6.99 (d, 3H, J¼7.1 Hz, H
H, J¼8.1 Hz, H ), 4.56 (t, 4H, J¼1.8 Hz, subs Cp), 4.54 (t, 4H,
J¼1.8 Hz, subs Cp), 4.25 (t, 4H, J¼1.8 Hz, subs Cp), 4.24 (t, 4H,
J¼1.8 Hz, subs Cp), 3.93 (s, 20H, Cp), 3.90 (s, 6H, CH S), 2.48 (q, 6H,
J¼7.4 Hz, SCH ), 2.21 (s, 3H, PhCH ), 1.28 (t, 9H, J¼7.4 Hz, CH
NMR (126 MHz, CD Cl (ppm) 143.71, 140.20, 138.29, 138.20,
37.29, 137.10, 133.63, 133.55, 132.13, 132.02, 130.95, 127.92, 124.74,
24.69, 122.22, 122.05, 120.02, 111.06, 89.69, 87.74, 86.52, 84.43,
2
O
3
: cyclohexane/CH
2
Cl
2
60:40) to give 14 as an orange solid
Cl )/nm 261 (163,200), 306 (127,500),
Cl (ppm) 8.07
, H ), 7.31 (d, 2H,
), 6.90 (d,
4
7, 8741–8744.
5. Vives, G.; Gonzalez, A.; Jaud, J.; Launay, J.-P.; Rapenne, G. Chem.dEur. J. 2007, 13,
5622–5631.
6. Moresco, F. Phys. Rep. 2004, 399, 175–225 and references therein.
7. Grill, L. J. Phys.: Condens. Matter 2008, 20, 053001.
l
max
(3
) (CH
2
1
2
1
2
2
) d
1
1
a
d
3
5
b
1
4
6
c
1
8. (a) Joachim, C.; Gimzewski, J. K.; Aviram, A. Nature 2000, 408, 541–548; (b)
Rosei, F.; Schunack, M.; Jiang, P.; Gourdon, A.; Lægsgaard, E.; Stensgaard, I.;
Joachim, C.; Besenbacher, F. Science 2002, 296, 328–331.
2
2
1
9. (a) Moresco, F.; Meyer, G.; Rieder, K. H.; Tang, H.; Gourdon, A.; Joachim, C. Phys.
Rev. Lett. 2001, 87, 088302; (b) Moresco, F.; Meyer, G.; Rieder, K. H.; Tang, H.;
Gourdon, A.; Joachim, C. Phys. Rev. Lett. 2001, 86, 672–675; (c) Rapenne, G.;
Jimenez-Bueno, G. Tetrahedron 2007, 63, 7018–7026; (d) Grill, L.; Rieder, K. H.;
Moresco, F.; Rapenne, G.; Stojkovic, S.; Bouju, X.; Joachim, C. Nat. Nanotechnol.
2
13
2
3
3
);
C
2
2
) d
1
1
2
007, 2, 95–98.
20. (a) Carella, A.; Jaud, J.; Rapenne, G.; Launay, J.-P. Chem. Commun. 2003, 2434–
435; (b) Carella, A.; Launay, J.-P.; Poteau, R.; Rapenne, G. Chem.dEur. J. 2008,
14, 8147–8156.
2
8
2
4.35, 63.85, 69.82, 69.22, 69.19, 66.44, 66.42, 66.38, 66.36, 36.58,
þ
5.37, 21.00, 14.43; MS (MALDI-TOF) m/z 1882.3 ([M ]); High res-
2
1. (a) Sonogashira, K.; Yatake, T.; Tohda, Y.; Takahashi, S.; Hagihara, N. J. Chem. Soc.,
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þ
olution LSI m/z 1883.3301 ([MþH] , 100%, calculated for
C
106 4 6 3
H94BFe N RuS : 1883.3236).
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G.V. thanks the French Ministry of National Education and the
Ecole Normale Sup e´ rieure of Lyon for a Ph. D. Fellowship. This work
was supported by the CNRS and the University Paul Sabatier
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edged for her comments and corrections on this manuscript.
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