Redox-active ruthenium(ii) σ-arylacetylide wires for molecular electronics incorporating insulating chains

Article abstract of DOI:10.1039/c1nj20235a

The preparation and properties of novel carbon-rich mono-, bi-, and tri-metallic ruthenium complexes terminated with protected thiol functions for further surface binding are reported. These new structurally rigid complexes include a short chain (SC) or a long (LC) saturated chain between the terminal linking functions and the conjugated carbon-rich pathway in order to increase contact resistance. They display low oxidation potential, and IR studies of the neutral complexes and of their various oxidized forms indicate the high bridging ligand implication in the oxidation processes and charge delocalization. These molecules are expected to facilitate coulomb blockade behaviour in molecular junctions, and are thus excellent candidates to contribute to the establishment of the structure-property relationships of metal containing molecular wires.

Full text of DOI:10.1039/c1nj20235a

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PAPER
Redox-active ruthenium(II) r-arylacetylide wires for molecular electronics
incorporating insulating chainsw
Ahmed Benameur, Pierre Brignou, Emmanuel Di Piazza, Yves-Marie Hervault,
´
Lucie Norel and Stephane Rigaut*
Received (in Montpellier, France) 14th March 2011, Accepted 29th April 2011
DOI: 10.1039/c1nj20235a
The preparation and properties of novel carbon-rich mono-, bi-, and tri-metallic ruthenium
complexes terminated with protected thiol functions for further surface binding are reported.
These new structurally rigid complexes include a short chain (SC) or a long (LC) saturated chain
between the terminal linking functions and the conjugated carbon-rich pathway in order to
increase contact resistance. They display low oxidation potential, and IR studies of the neutral
complexes and of their various oxidized forms indicate the high bridging ligand implication in the
oxidation processes and charge delocalization. These molecules are expected to facilitate coulomb
blockade behaviour in molecular junctions, and are thus excellent candidates to contribute to the
establishment of the structure–property relationships of metal containing molecular wires.
metal dp and the appropriate p-orbital of the carbon-rich
ligands.
Following the ‘‘bottom-up’’ approach expressed by Feynman
Introduction
The understanding and control of electron transfer reactions
constitute major challenges in science as it is a fundamental
process to numerous complex chemical systems ranging from
life processes to electronic devices. Therefore, metal complexes
displaying ligand-mediated electronic effects have attracted
increasing interest.1–4 In particular, several wire-like transition
metal complexes with direct s-bond connection of the carbon-
rich bridges with the metal atoms have shown excellent
abilities to provide a strong electronic interaction between
the remote redox-active metal centers.4 The role of the metallic
moieties within the bridge has also been considered, and the
exceptional ability of ruthenium to operate as a connector
allowing electron flow to occur between different elements in
trans-ditopic carbon-rich systems, in contrast to other metals
such as platinum, was highlighted.5–8 In particular, with the
fragment [RuCl2(dppe)2] (dppe = 1,2-bis(diphenylphosphino)-
ethane), we realized polynuclear ‘‘W’’-shaped molecular wires,
up to 28 A long, and with three similar metal centres prevent-
ing single electron trapping on one part of the structure in
different oxidation/reduction states, i.e. with a spin density
uniformly distributed between the metal atoms and the carbon
atoms of the chains.8,9 The underlying reason for the involvement
of the carbon-rich ligands in the redox processes is the lower
energy of the Ru 4d orbitals leading to a higher ligand
character of the HOMO resulting from the overlap of the
in 1959 proposing that atoms can be arranged in a manner to
build circuits of a few thousands of Angstroms across,10–12 the
¨
molecular wire is the simplest component, with the sole function
of facilitating the passage of current between two points.
Understanding of charge transport through molecular wires
on molecular length in metal–molecule–metal junctions is a
thus central issue (e.g., tunnelling versus hopping).12 Because
potential molecular wires display properties strongly connected
to their structure, carbon-rich metal complexes allowing
intramolecular electron-transfer with easily accessible redox
state are objects of special interest. Several studies have been
performed to probe their electrical conductivity that show
that ruthenium carbon-rich complexes display interesting
behaviours and a higher conductance over platinum adducts
and related organic analogues.13–17 For instance, studies of
electronic transport through self-assembling of diruthenium(III)
tetra(2-anilinopyridinate)-di(4-thiolphenylethynyl) trans-[Ru2(ap)4-
((CRCC6H4)nS–)2] (n = 1, 2) molecules in nanogap molecular
junctions confirmed that devices employing such redox-active
molecules allow resonant tunnelling, along with observation of
hysteresis in I–V traces possibly due to charge storage in the
molecules.15 With the ‘‘RuCl(dppe)2’’ system, using conducting
probe atomic force microscopy (CP-AFM) and crossed-wire
(X-wire) junctions, we probed the electrical transport behaviour
of a series of redox-active ruthenium bis(s-arylacetylide) wires
Run (n = 1À3) as a function of molecular length (Scheme 1).16,18
At room temperature, a very weak dependence of the wire
resistance with molecular length (b = 0.09 AÀ1) was found,
consistent with a high degree of electronic coupling along the
´
Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite de
Rennes 1, Campus de Beaulieu, F-35042, Rennes Cedex, France.
E-mail: stephane.rigaut@univ-rennes1.fr
w Dedicated to Prof. Didier Astruc on the occasion of his 65th
birthday.
c
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Results and discussion
Synthesis of the bis(r-arylacetylide) complexes
The synthetic strategy to achieve the targeted complexes
bearing the two short (SC) or the two long (LC) chains
terminated with protected thiol functions requires the use of
the terminal alkynes [H–CRC–1,4-C6H4–CH2–SAc] (1a)22
and [H–CRC–1,4-C6H4–O–(CH2)6–SAc] (1b). The latter is
obtained in four steps from 4-iodophenol (Scheme 2). After
formation of the ether from 1,6-dibromo hexane,23 the
procedure is in fact similar to that used to obtain 1a, i.e. with
(i) formation of the corresponding thioester 2 in the presence
of potassium thioacetate, (ii) subsequent Sonogashira coupling
with trimethylsilylacetylene to obtain the protected alkyne 3,
and (iii) alkyne deprotection with Bu4NF.
Scheme 1 Ruthenium wires and charge transport mechanisms (5 K):
(a) direct tunnelling for Ru1 and Ru2 junctions, (b) sequential tunnel-
ling for the Ru3 junction.
molecular backbone, and associated with a high contact resis-
tance. In low temperature (5 K) experiments, direct tunnelling is
found to be the dominant transport mechanism in the short
junctions (2.4 and 3.6 nm for n = 1 and 2) that fall within the
length range where this mechanism is expected to prevail. The
electron crosses the junction in a single step with no appreciable
time of residence on the molecule (Scheme 1a). In contrast,
coulomb blockade-like behaviour (charge injection) was observed
in junctions incorporating the trimetallic adduct (4.9 nm). Due to
the small EF – EHOMO offset (0.25 V), the Au Fermi level of one
contact comes into resonance with molecular levels (HOMOs)
and facilitates direct charge injection from the Au electrodes into
the wire at low voltages (sequential tunnelling, Scheme 1b).
Taken as a whole, these results gave us impetus to design
related oligomeric carbon-rich ruthenium molecular wires that
would allow the formation of alternative molecular junctions
with increased contact resistance that is expected to enhance
charge injection in the molecule. Therefore, we would expect
from such molecules, via the study of charge transport behavior;
the deeper understanding of (i) the coulomb blockade-like
behavior, and (ii) the high contact resistance of Run molecules.
This last point is also an interesting finding in the light that, in
general, a low contact resistance is expected from the small
energy offsets.
The reaction leading to SCRu1SC and LCRu1LC is dis-
played on Scheme 3. According to the general procedure
previously developed in the laboratory to obtain bis(s-aryl-
acetylide) complexes,24 the preparation of the two mono-
metallic targeted complexes was readily achieved with the
use of cis-[(dppe)2RuCl2] and of the appropriate alkyne 1a
or 1b in the presence of a non-coordinating salt (NaPF6) and a
base (Et3N) to afford SCRu1CS and LCRu1LC in 86% and
66% yield, respectively.
As shown in Scheme 4, the corresponding bimetallic adducts
SCRu2SC and LCRu2LC were obtained from the 16-electron
species [(dppe)2RuCl][OTf] and diethynylbenzene through the
bis(vinylidene) 4. The latter was not isolated owing to its
insolubility and its sensitivity to deprotonation. Thus, it was
directly reacted with the terminal alkynes 1a–b using the
classical reaction consisting, after deprotonation of 4 with
Et3N, in the substitution of the chlorine atoms with the
appropriate alkyne bearing the linking group to afford
SCRu2SC and LCRu2LC in 67% and 63% yield, respectively.
Finally, the trimetallic wires SCRu3SC and LCRu3LC were
achieved by using complex 6 bearing two activable alkyne
functions25 as a central core (Scheme 5). With the help of the
We report herein the synthesis, the optical and electro-
chemical properties of two new series of linear ruthenium(II)
bis(s-arylacetylide) complexes, SCRunSC and LCRunLC
(n = 1À3), terminated by protected thiol functions for further
surface binding (Scheme 1). These molecules include two short
(SC) or two long (LC) saturated chains between the terminal
linking functions and the conjugated carbon-rich pathway
to increase contact resistance between the electrodes and
the central conjugated core. These wires still contain one to
three metal centers connected by 1,4-diethynylbenzene because
of the ready availability of the parent alkyne, the low
oxidation potentials of the resulting ruthenium s-aryl-
acetylides compared to organic molecules, the large separation
of the reversible oxidation waves in bimetallic and trimetallic
complexes indicating the chemical and thermodynamic stability
of these easily accessible redox states, and its excellent ability
to electronically couple the metal units.18–21 In addition, we
provide IR studies of the different redox states to get more
detailed insight in the oxidation processes and the charge and
spin delocalization.
Scheme 2 Synthetic procedure for 1b.
Scheme 3 Synthetic path yielding to SCRu1SC and LCRu1LC.
c
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bis(s-arylacetylide) species and of the trans disposition of two
carbon-rich chains on each ruthenium centers, thus showing
the full substitution processes. For the trimetallic adducts, two
peaks with a 2 : 1 intensity ratio fully support the structure
with one central ruthenium unit and two peripheral units. In
the 13C NMR spectra, the characteristic quintet (2JCP = 15 Hz)
signal corresponding to the a-acetylide carbon atom was
detected in most cases, and the IR spectra reveal intense nCRC
bands around 2060 cmÀ1. The presence of the acetyl protecting
groups for the thiol functions is also evidenced with IR
(n(CQO) = 1686 cmÀ1) and 1H NMR (d E 2.3 ppm)
spectroscopies.
Scheme 4 Synthetic procedure for SCRu2SC and LCRu2LC.
UV-visible spectra
In addition to the intense short-wavelength absorption bands
for transitions involving the dppe ligand (intra ligand transi-
tions), all the bis-acetylide complexes show a broad absorption
band with a large extinction coefficient at lower energy around
340–380 nm (Table 1, Fig. 1). For the parent mono(s-aryl-
acetylide) complexes trans-[ClRu(dppe)2–CRC–C6H4–R]
(R = NO2, H, OMe, NMe2),26 these transitions appear to
be multiconfigurational MLCT excitations involving metal- and
chloride-based MOs toward aryl-based p* MOs, except when
R = OMe. In that case, the most intense transition involves a
dominant charge transfer contribution from metal-centered
MOs toward p* MOs located on the phosphorus. Therefore,
resulting from a considerable mixing of Ru(dp) orbitals with
alkynyl p-orbitals, the present low energy transitions should
present a RuII(dp) - L(p*) (MLCT) character admixed with a
moderate to strong p - p* (IL) nature, probably including p*
MOs located on the phosphorus for the LCRunLC compounds
Scheme 5 Synthetic pathways yielding to SCRu3SC and LCRu3LC.
with the ether chains. These MLCT bands present
a
vinylidene complexes 5a–b obtained from [(dppe)2RuCl][OTf]
and from the accurate alkyne 1a–b, the targeted molecule
SCRu3SC and LCRu3LC are achieved in good yield with the
usual procedure (67% and 63%, respectively). It should be
noted that this strategy provides a more convenient and
straightforward route to such symmetric species than that we
previously reported.18
The wires were characterized by means of 31P, 1H, 13C
NMR, IR, and mass spectroscopies, as well as with elemental
analysis. For the mono and bimetallic wires, particularly
informative is the single resonance peak in the 31P NMR
spectra at ca. d = 55 ppm. This signal is characteristic of
Fig. 1 Electronic absorption spectra for SCRunSC (n = 1–3), in
CH2Cl2.
Table 1 Electrochemical (CV) and UV-vis data
Electrochemistrya
UV-Vise
E1/V
l )
max/nm (e/molÀ1 L cmÀ1
SCRu1SC
LCRu1LC
SCRu2SC
LCRu2LC
SCRu3SC
LCRu3LC
À0.023
À0.170
À0.265
À0.294
À0.297
À0.322
0.837b
230 (65 200), 344 (39 900)
228 (82 400), 310 (41 300)
226 (119 900), 376 (65 000)
230 (92 000), 375 (36 000)
230 (173 600), 382 (122 600)
231 (135 000), 380 (33 600)
0.772b
0.052
À0.006
À0.120
À0.175
0.821c 1.002b
0.577c 0.844b
0.592c 0.958b
0.593d 0.809b
0.091
0.053
a
Sample 1 mM, Bu4NPF6 (0.2 M) in CH2Cl2, v = 100 mV sÀ1, potentials are reported in V vs. the ferrocene/ferrocenium couple, reversible
b
c
d
oxidation processes, DEp E 60–70 mV. Peak potential of an irreversible process. DEp E 85–95 mV. Peak potential of a partially reversible
process. In CH2Cl2.
e
c
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bathochromic shift when the length of the molecule is
increased consistent with an enlargement of the conjugated
path length through the ruthenium moieties, as probed by the
Franck–Condon absorption event.27
longer bridging ligand.20 For the closely related ‘‘W’’ shaped
compounds,9 this phenomenon was, at least in part, connected
to the delocalisation of the frontiers orbitals, allowing unpaired
electrons to spread over the whole conjugated path. A similar
electronic delocalization is expected to occur in the present
molecular wires. Note that, as previously observed,16 it is
expected that the high lying (easily oxidized) HOMO level will
bring about improved energy level alignment with the Au
Fermi level.
Electrochemical data
In order to probe the ability of these new conjugated species to
be oxidized in molecular junctions, cyclic voltammetry traces
(CVs) were recorded (CH2Cl2 solutions, 0.2 M Bu4NPF6). The
values of the potentials are reported in Table 1, and typical
CVs are displayed in Fig. 2. In agreement with related
complexes,9,18–20 the number of electrochemical processes
observed at low potential is related to the number of ruthenium
units present in the molecules. One or two processes, most
often not fully reversible, are also observed at higher potential
and are consistent with an undergoing chemical reaction of
those oxidized species. For our purpose, we particularly
focused our attention on the fully reversible processes at low
potential. The two monometallic compounds SCRu1SC and
LCRu1LC undergo one electron oxidation at low potential,
usually erroneously viewed as essentially involving the RuIII/RuII
couple whereas it actually strongly involves the carbon-rich
ligand.4a,f,9,26 Indeed, as an illustration, with the parents trans-
[ClRu(dppe)2–CRC–C6H4–R] (R = NO2, H, OMe, NMe2),
the spin density (DFT) for the metal atom only range from
0.4 eÀ (X = NO2) to 0.2 eÀ (X = NMe2).26 Note that the
potentials reported here are consistent with the oxidation
potential of the parent Ru(dppe)2(–CRC–Ph)2 complex
(E1 = À0.05 V vs. FcH/FcH+) by taking into account the
respective electronic effects of the long and short chains on the
carbon rich ligands.
Characterization of the oxidized species: IR spectroscopy
In this part, we focused our attention on the reversible
oxidation processes at low potential and on the SCRunSC
series only. Therefore, the IR properties of SCRunSC (n = 1–3)
were investigated by means of IR spectro-electrochemistry
(SEC) in an Optically Transparent Thin-Layer Electrochemical
(OTTLE) cell, and the resulting data are gathered in Table 2.
Fig. 3a shows the evolution of the IR spectrum of SCRu1SC
upon electrochemical oxidation. We observe a substantial
Table 2 Characteristic IR data for SCRu1SC, SCRu2SC and
SCRu3SC in their various oxidation states (1,2-C2H4Cl2/NBu4PF6
(0.2 M))
nCRC
Aryla
SCRu1SC
[SCRu1SC]+
SCRu2SC
2061(m)
2061(w), 1902(m)
2059(m)
2059(m), 1964(vs)
2026(m), 1910(m)
2058(m)
2058(m), 1962(s), 1852(s)
2052(m), 1959(s), 1904(s)
2015(m), 1961(m), 1907(m)
1601
1580(m)
—
1563(m)
—
1591, 1563, 1528(ws)
1540(m)
1550(s)
—
[SCRu2SC]+
[SCRu2SC]2+
SCRu3SC
[SCRu3SC]+
[SCRu3SC]2+
[SCRu3SC]3+
The bi- and tri-metallic complexes SCRunSC and LCRunLC
(n = 2, 3) display two and three redox processes, respectively,
at low potential. The large separation of the first two or three
processes for both compounds (DE1 E 300 mV, Kc = exp
(DE1F/RT) = 1.5 Â 105) establishes that all of the considered
oxidized species are stable in solution with respect to dispro-
portionation but is not a mere reflection of the interaction
between the redox centres.28 However, note that the observed
first (n = 2, 3) and second (n = 3) oxidation potentials are
lower than the first oxidation potential of the monometallic
congeners. This fact supports the idea that the present oxidized
species gain considerable stabilization, not observed for a
a
Combinations of CQC stretching and CH-bending modes.
Fig. 3 Spectroscopic changes observed in the IR region upon oxida-
tion in an OTTLE cell (1,2-C2H4Cl2, 0.2 M Bu4NPF6) of (a) SCRu1SC
to [SCRu1SC]+, (b) [SCRu2SC]n+ (n = 0 to 2), (c) [SCRu3SC]n+
Fig. 2 CV traces obtained for LCRunCL (n = 1–3), in CH2Cl2
(Bu4NPF6, 0.1 M); v = 200 mV sÀ1
.
(n = 0 to 2), (d) [SCRu3SC]2+ to [SCRu3SC]3+
.
c
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bleaching of the nCRC band at 2061 cmÀ1 with the concomitant
emergence of a new stretching band of similar intensity at
1902 cmÀ1, along with the growth of phenylene based absorption
at 1580 cmÀ1 showing the implication of the phenyl groups.20
The observed behavior is thus consistent with a participation
of both acetylide ligands to the oxidation process, resulting in
a weakening of the CRC bond, and also affecting the
aromatic ring (allenylenic contribution). The remaining small
vibration at 2061 cmÀ1 in the oxidized state could account for
an incomplete delocalisation of the vacancy from one ligand to
the other on the IR time scale (i.e. class II type contribution).2,29
Note that for all oxidation events and complexes, the nCQO
stretching of the thioacetate group remains unaffected, as
expected for a function outside the conjugated path. For the
bimetallic complex SCRu2SC (Fig. 3b), the first oxidation
process is accompanied by the decrease of the intensity of
the nCRC band at 2059 cmÀ1 along with the growth of a very
intense band at 1964 cmÀ1. An intense band at 1563 cmÀ1 is
also observed for a phenylene based vibration of [SCRu2SC]+.
This behaviour is consistent with that of the parent compound
[Cl(dppe)2Ru–CRC–C6H4–CRC–Ru(dppe)2Cl]+ also including
a remaining nCRC contribution at 2059 cmÀ1 that thus can be
explained by incomplete delocalisation of the vacancy on the
IR time scale over the bridge (mixed class II and class III
behaviours), rather than from the different contributions of
internal and external carbon-rich ligands.20 Furthermore, the
shoulders observed in the main band of [SCRu2SC]+ corres-
ponding to the vibration of [SCRu2SC]2+ (vide infra) support
orbitals relevant for oxidation is increased with molecular
length, and are consistent with the stabilization of the oxidized
states going from SCRu1SC to SCRu3SC, according to the
observed lowering of oxidation potentials.
Conclusions
In this work, we have synthesized two novel series of ruthe-
nium carbon-rich compounds for molecular electronics. These
ruthenium(II) s-arylacetylide complexes with short or long
saturated chains between the terminal linking functions and
the structurally rigid conjugated carbon-rich pathway will
allow for the building of new molecular junctions including
one, two, or three metal centers. Cyclic voltammetry reveals
the presence of low oxidation potentials, and IR studies of the
various oxidized forms reveal that metal genuine oxidations
are not observed and point out the implication of the bridging
ligand in the oxidation processes. All these factors are
expected to enhance sequential tunneling within molecular
junction (e.g. of direct charge injection into the molecular
wires), and to give valuable insights into the structure–
property relationships of metal containing molecular wires.
This area is likely to undergo further developments in the
future as original properties and high levels of functionality
may also be integrated into such a molecular system through
molecular engineering. For example, redox or photochemical
addressing of the molecular component for the realization of
multifunctional conductive switches could be achieved with
appropriate combinations of such types of organometallics
with functional units.30
this hypothesis. Upon further oxidation to [SCRu2SC]2+
,
bleaching of the nCRC band at 2059 cmÀ1 is observed with
the emergence of two new main absorption bands at 2026 and
1910 cmÀ1. A similar nCRC band around 1910 cmÀ1 is also
present for the bicationic parent compound and consistent
with a cumulenic central structure, while the other nCRC
absorption, not observed for the parent compound, is tenta-
tively ascribed to the external carbon-rich ligands with a more
acetylide character and thus having a reduced, but still present,
participation to the delocalisation of the charge. For the
trimetallic species SCRu3SC, the first oxidation leads to two
new bands at 1962 and 1852 cmÀ1, whereas the initial vibration
at 2058 cmÀ1 remains unaffected (Fig. 3c). During the second
oxidation, while the two other vibrations are still present, the
one at 1852 cmÀ1 shifts to 1904 cmÀ1. Importantly, note that
the vibrations characteristic of the phenylene unit(s) increases
upon both oxidations. All the vibrations are difficult to
rationalize here, however, the remaining acetylide contribution
could still account for an incomplete delocalisation of the
vacancy from one ligand to the other on the IR time scale. The
cumulenic and phenylene character enhancement with oxidations
also suggests amplification, in terms of size and probably
magnitude, of the implicated conjugated pathway possibly
because of the charging of some of the acetylide moieties
which generates a larger change of molecular dipole moment
during the stretching vibrations. Upon the third oxidation to
[SCRu3SC]3+, all the vibrations vanish, as observed for other
charged species,9 possibly as a result of a weaker change in
dipolar moment upon vibration in this highly charged species
(Fig. 3d). In conclusion, for the three species, these observations
suggest that the role of the conjugated path in the molecular
Experimental
Materials
The reactions were carried out under an inert atmosphere using
the Schlenk techniques. Solvents were freshly distilled under
argon using standard procedures. [(dppe)2RuCl](OTf),31
cis-[(dppe)2RuCl2],32 [H–CRC–1,4-C6H4–CH2–SAc] (1a),22
[I–1,4-C6H4–O–(CH2)6–Br],23 and [HCRC–p-C6H4–CRCH]33
were prepared as previously reported.
Instruments
Electrochemical studies were carried out under argon using
an Eco Chemie Autolab PGSTAT 30 potentiostat (CH2Cl2,
0.2 M Bu4NPF6), the working electrode was a Pt disk and
ferrocene the internal reference. IR spectroelectrochemistry
(SEC) experiments were performed at 201C, under argon, with
a home-made Optically Transparent Thin-Layer Electro-
chemical (OTTLE) cell, path length = 1 mm, using a Bruker
IFS28 spectrometer and an EG&G PAR model 362 potentiostat.
A Pt mesh was used as the working electrode, a Pt wire as the
counter electrode, and an Ag wire as a pseudo-reference
electrode. The electrodes were arranged in the cell such that
the Pt mesh was in the optical path of the quartz cell. The
anhydrous freeze-pump-thaw degassed sample-electrolyte
solution (0.2 M n-Bu4NPF6) was cannula-transferred under
argon into the cell previously thoroughly deoxygenated. At the
end of the experiments, the original spectra were regenerated
c
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(ca. 95–100%). In every case re-reduced or re-oxidized samples
displayed in the spectral region of interest no features other
than those of the parent material. High resolution mass
spectra (HRMS) were recorded in Rennes at the CRMPO
purified by column chromatography on silica gel with a 2 : 3
pentane/dichlomethane mixture as an eluant to give 225 mg of
1b as a white solid (81%). 1H NMR (200 MHz, CDCl3,
3
3
297 K): d = 7.44 (d, J = 8.8 Hz, 2H, HAr), 6.84 (d, J =
8.8 Hz, 2H, HAr), 3.97 (t, 3J = 6.4 Hz, 2H, O–CH2), 3.01
(s, 1H, CRCH), 2.90 (t, 3J = 6.5 Hz, 2H, S–CH2), 2.35
(s, 3H, CH3), 1.83–1.47,(m, 8H, CH2). 13C NMR (75 MHz,
CDCl3, 297 K): 197.44 (CQO), 159.88 (O–Cq), 134.00 (CArH),
114.86(CArH), 114.35 (RC–Cq), 84.18 (H–CRC), 76.12
(H–CR), 68.26 (O–CH2), 31.10(CH3), 29.88 (CH2), 29.44
(CH2), 28.93 (CH2), 26.00 (CH2). IR (KBr): n (cmÀ1) =
1682 (CQO), 2102(CRC), 3235(RC–H). HR-MS EI
(m/z): 276.1199 ([M+], calcd: 276.11840). Elemental analysis
(%) for C16H20O2S: C, 69.53; H, 7.29; S, 11.60 (calcd: C,
69.79; H, 7.36; S, 11.50).
(Centre Regional de Mesures Physiques de l’Ouest) on a
´
ZabSpecTOF (LSIMS at 4 kV) spectrometer.
Synthesis
I–C6H4–O–(CH2)6–SAc (2). In
a
Schlenk tube,
I–C6H4–O–(CH2)6–Br (2.138 g, 5.58 mmol), and KSAc
(0.637 g, 5.58 mmol) were dissolved in acetone (5 mL). The
solution was stirred during 40 h at room temperature. The
solution was poured in water (50 mL) and extracted with
diethyl ether (3 Â 30 mL). The combined extracts were washed
with water and dried with MgSO4. The filtrate was evaporated
to dryness gave to 1.92 g of 2 as a white solid (91%). 1H NMR
(200 MHz, CDCl3, 297 K): d = 7.56 (d, 3JHÀH = 8.8 Hz, 2H,
trans-[AcS–CH2–C6H4–CRC–Ru(dppe)2–CRC–C6H4–CH2–
H
Ar), 6.69 (d, 3J = 8.8 Hz, 2H, HAr), 3.92 (t, 3JHÀH = 6.5 Hz,
SAc] (SCRu1SC). In
a Schlenk tube, cis-(dppe)2RuCl2
3
2H, O–CH2), 2.90 (t, JHÀH = 6.5 Hz, 2H, S–CH2), 2.34
(s, 3H, CH3), 1.82–1.46 (m, 8H, CH2). 13C NMR (75 MHz,
CDCl3, 297 K 3): d = 196.45 (CQO), 159.35 (O–Cq–), 138.57
(CArH), 117.31 (CArH), 82.90 (I–Cq), 68.29 (O–CH2–), 31.10
(CH3), 29.86 (CH2), 29.42 (CH2), 29.40 (CH2), 28.90 (CH2),
28.66 (CH2),25.97 (CH2). IR (KBr): n (cmÀ1) = 1677 (CQO).
HR-MS EI (m/z): 378.0162 ([M+], calcd: 378. 01505).
Elemental analysis (%) for C14H19O2IS: C, 44.45; H, 5.06; S,
8.48 (calcd: C, 44.23; H, 5.06; s, 8.55).
(223 mg, 0.230 mmol) and NaPF6 (154 mg, 0.920 mmol) were
introduced. In another tube 4a (132 mg, 0.690 mmol) was
dissolved in CH2Cl2 (30 mL). This solution was slowly added
to the fist one and Et3N (0.190 mL) were added quickly to the
solution. The mixture was further stirred during 3 days at
room temperature. After filtration, the solution was evapo-
rated and then the residue was washed with pentane (20 mL).
The solution was filtered through a plug of alumina eluting
with CH2Cl2. Evaporation of the solvent led to a yellow solid
182 mg (62%) (6b). 31P{1H} NMR (121 MHz, CDCl3, 297 K):
d = 53.4 (s,PPh2). 1H NMR (200 MHz, CDCl3, 297 K)
d = 6.98–7.55 (m, 48H, HAr), 4.12 (s, 4H, S–CH2), 2.65
(m, 8H, P–CH2), 2.41 (s, 6H, CH3). 13C NMR (75 MHz,
Me3Si–CRC–C6H4–O–(CH2)6–SAc (3). In a Schlenk tube,
a suspension of 2 (0.948 g, 2.5 mmol), trimethylsilylacetylene
(0.53 mL), Pd(PPh3)2Cl2 (15 mg, 0.0165 mmol), and CuI
(34 mg, 0.138 mmol) in ethyldiisopropylamine (4 mL) and
THF (4 mL) was heated at 45 1C for 72 h. The reaction
mixture was filtered, the solid washed with ether (50 mL), and
the combined organic solutions were evaporated to dryness.
The residue was further purified by column chromatography
on silica gel with a 1 : 1 pentane/dichlomethane mixture as an
CD2Cl2, 297 K): d = 195.16 (CQO), 137.17–112.43 (CAr),
2
132.43 (quint., JPC
= 15 Hz, Ru–CRC–), 116.17
(Ru–CRC–), 33.45 (CH3), 31.40 (m, |1JPC+3JPC| = 24 Hz,
PCH2CH2P), 30.23 (CH2). IR (KBr): n (cmÀ1) = 1686
(CQO), 2061(CRC). HR-MS FAB+ (m/z): 1276.2558
([M+] calcd: 1276.24983). Elemental analysis (%) for
C74H66O2S2P4Ru: C, 69.92; H, 5.33; S, 5.09 (calcd: C, 69.63;
H, 5.21; S, 5.02).
1
eluant to give 3 (678 mg, 78%). H NMR (200 MHz, CDCl3,
3
297 K) : d = 7.41 (d, JHÀH = 8.8 Hz, 2H, HAr), 6.82
3
3
(d, JHÀH = 8.8 Hz, 2H, HAr), 3.96 (t, JHÀH = 6.4 Hz,
3
2H, O–CH2), 2.90 (t, JHÀH = 6.5 Hz, 2H, S–CH2), 2.34
trans-[AcS–(CH2)6–O–C6H4–CRC–Ru(dppe)2–CRC–C6H4–
O–(CH2)6–SAc] (LCRu1LC). With an identical procedure,
cis-(dppe)2RuCl2 (164 mg, 0.17mmol), NaPF6 (114 mg,
0.68mmol), and 1b (138 mg, 0.5mmol) led to 210 mg of
(s, 3H, CH3), 1.82–1.45 (m, 8H, CH2), 0.25 (s, 9H, (CH3)3).
13C NMR (75 MHz, CDCl3, 297 K): d = 196.45 (CQO),
159.68 (O–Cq), 133.88 (CArH), 115.45 (RC–Cq),
114.74 (CArH), 105.68 (Si–RC–), 96.76 (Si–CR), 68.23
(O–CH2–), 31.11(CH3), 29.88 (CH2), 29.45 (CH2), 28.94
(CH2), 26.00 (CH2), 0.53 (CH3–Si). IR (KBr): n (cmÀ1) =
1690 (CQO), 2151 (CRC). HR-MS EI (m/z): 348. 1588
([M+], calcd: 348.15793). Elemental analysis (%) for
C19H28O2SiS: C, 65.47; H, 8.10; S, 9.20 (calcd: C, 65.59; H,
8.20; S, 9.23).
a
yellow solid (65%). 31P{1HR NMR (121 MHz,
CDCl3, 297 K): d = 55.2 (s, PPh2). 1H NMR (200 MHz,
CDCl3, 297 K): 6.71–7.53 (m, 48H, HAr), 3.94
d
=
3
3
(t, JHÀH = 6.3Hz, 4H, O–CH2), 2.94 (t, JHÀH = 7.1 Hz,
4H, S–CH2), 2.63 (m, 8H, P–CH2), 2.34 (s, 6H, CH3),
1.52–1.81 (m, 16H, CH2). 13C NMR (75 MHz, CD2Cl2,
297 K): d = 195.61 (CQO), 155.40–113.69 (CAr), 115.38
(Ru–CRC–), 67.78 (O–CH2–), 31.46 (m, |1JPC+3JPC| =
24 Hz, PCH2CH2P), 30.46 (CH3), 29.54 (CH2), 29.27 (CH2),
28.99 (CH2), 28.56 (CH2), 25.64 (CH2). IR (KBr): n (cmÀ1) =
1693 (CQO), 2068 (CRC). HR-MS FAB+ (m/z): 1448.4001
([M+] calcd: 1448.3961). Elemental analysis (%) for
C84H86O4S2P4Ru: C, 69.37; H, 6.01; S, 4.32 (calcd : C,
69.64; H, 5.98; S, 4.43).
H–CRC–C6H4–O– (CH2)6–SAc (1b). In a Schlenk tube, 3
(348 mg, 1 mmol) and Bu4NF (0.1 M in THF, 1.5 mL) were
dissolved in THF (15 mL). The solution was stirred during
90 min at room temperature, then diluted with water (1.5 mL)
and evaporated to dryness. The residue was dissolved in water
and extracted with ether (3 Â 30 mL). The combined organic
solutions were evaporated to dryness. The residue was further
c
2110 New J. Chem., 2011, 35, 2105–2113
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3
trans-[ClRu(dppe)2QCQCH–C6H4–HCQCQRu(dppe)2Cl]
[TfO]2 (4). In a Schlenk tube, A mixture of diethynylbenzene
(25.2 mg, 0.2 mmol) and [(dppe)2RuCl][OTf] (432.6 mg,
0.4 mmol) in CH2Cl2 (20 mL) was stirred for 24 h at room
temperature. The precipitate was filtered and washed with cold
distilled CH2Cl2 (3 Â 20 mL). The solid was pumped dry to
afford an almost insoluble air sensitive green powder used as it
was without further purification for the next step (324 mg, 71%).
31P{1H NMR (121 MHz, CDCl3, 297 K): d = 36.6 (s, PPh2).
(d, 2H, JHÀH
=
8.0Hz, C6H4–R), 4.10 (br s, 1H,
RuQCQCH), 3.92 (s, 2H, CH2), 2.92 (m, 8H, P–CH2), 2.37
(s, 3H, CH3). 13C NMR (75 MHz, CD2Cl2, 297 K): d = 354.27
2
(quint., JPC
= 14 Hz, RuQCQC–), 194.75 (CQO),
135.72–124.93 (CAr), 108.98 (RuQCQC–), 32.88 (CH3),
30.15 (CH2), 28.68 (m, |1JPC+3JPC| = 23 Hz, PCH2CH2P).
IR (KBr): n (cmÀ1) = 1687 (CQO), 1642 (QCQC). HR-MS
FAB+ (m/z): 1123.1905 ([M+] calcd: 1123.1891). Elemental
analysis (%) for C64H58O4F3ClP4S2Ru: C, 60.40; H, 4.59; S,
5.04 (calcd: C, 59.97; H, 4.72; S, 4.77).
trans-[AcS–CH2–C6H4–CRC–Ru(dppe)2–CRC–C6H4–CR
C–Ru(dppe)2–CRC–C6H4–CH2–SAc] (SCRu2SC). In a Schlenk
tube, 4 (230 mg, 0.10 mmol), NaPF6 (67 mg, 0.4 mmol), 1a
(57 mg, 0.3 mmol) were introduced with CH2Cl2 (30 mL) and
triethylamine (0.6 mL, 50 eq.). The reaction mixture was stirred
4 days at room temperature. The solvent was then pumped dry
and the residue was washed with pentane (20 mL). Further
dissolution in CH2Cl2 (20 mL), filtration through a plug alumina
eluting with CH2Cl2 and evaporation of the solvent led to 154 mg
of a yellow powder (67%). 31P{1H} NMR (121 MHz, CDCl3,
297 K): d = 54.95 (s, PPh2). 1H NMR (200 MHz, CDCl3,
297 K): d = 7.61–6.63 (m, 92H, HAr), 4.14 (s, 4H, S–CH2), 2.68
(m, 16 H, P–CH2), 2.42 (s, 6H, CH3). 13C NMR (75 MHz,
CD2Cl2, 297 K): d = 195.18 (CQO), 137.24–125.60 (CAr), 117.64
(Ru–CRC–), 33.47 (CH3), 31.47 (m, |1JPC+3JPC| = 24 Hz,
PCH2CH2P), 30.23 (CH2). IR (KBr): n (cmÀ1) = 1688 (CQO),
2057 (CRC). HR-MS FAB+ (m/z): 4298.4652 ([M+] calcd:
trans-[Cl(dppe)RuQCQC(H)–C6H4–O–(CH2)6–SAc][TfO] (5b).
With an identical procedure, [(dppe)2RuCl][OTf] (541 mg,
0.54mmol) and 1b (276 mg, 1 mmol) led to 530 mg of a green
solid (87%). 31P{1H} NMR (121MHz, CDCl3, 297 K): d =
39.9 (s, PPh2). 1H NMR (CDCl3, 200 MHz, 297 K): d =
3
7.51–7.05 (m, 40H, HAr), 6.38 (d, JHÀH = 8.6Hz, 2H,
3
C6H4–R), 5.72 (d, JHÀH = 8.6Hz, 2H, C6H4-R), 3.85
3
(t, JHÀH = 6.4Hz, 2H, O–CH2–), 3.78 (br s, 1H, CQC–H),
2.9 (m, 8H, CH2 dppe), 2.36 (s, 3H, CH3) 1.78–1.47 (m, 8H,
CH2). RMN 13C (75M Hz, CD2Cl2, 297 K): d 357.31 (quint.,
2JPC = 14 Hz, RuQCQC–), 195.65 (CQO), 157.68–114.41
(CAr), 108.79 (RuQCQC–), 67.86 (O–CH2–), 30.46 (CH3),
29.52 (CH2), 29.02 (CH2), 28.91 (CH2), 28.70 (CH2), 28.55
(m, |1JPC+3JPC| = 24 Hz, PCH2CH2P), 28.49 (CH2), 25.51
(CH2). IR (KBr): n (cmÀ1) = 1686 (CQO), 1642 (QCQC).
HR-MS FAB+ (m/z): 1208.2576 ([(M
À
H)+] calcd:
2298.45613). Elemental analysis (%) for
C136H118O2S2-
1208.25443). Elemental analysis (%) for C69H68ClF3O5S2P4Ru:
C, 60.72; H, 5.07; S, 4.70 (calcd: C, 60.99; H, 50.4; S, 4.72).
P4Ru2.CH2Cl2: C, 70.38; H, 5.26; S, 2.37 (calcd: C, 70.04; H,
5.12; S, 2.74).
trans-[AcS–CH2–C6H4–CRC–Ru(dppe)2–CRC–C6H4–CR
C–Ru(dppe)2–CRC–C6H4–CRC–Ru(dppe)2–CRC–C6H4–
CH2–SAc] (SCRu3SC). In a Schlenk tube, 5a (332 mg,
0.26 mmol), NaPF6 (88 mg, 0.52 mmol), 6 (150 mg, 0.13 mmol)
were introduced, and CH2Cl2 (30 mL) was added. Then, triethyl-
amine (1 mL, 25 eq.) was added. The reaction mixture was stirred
4 days at room temperature and the solvent was pumped dry.
The residue was dissolved in CH2Cl2 (30 mL), and the mixture
was washed with water (3 Â 20 mL). After drying (MgSO4), it
was concentrated under reduced pressure, and washed with
pentane (3 Â 20 mL) to afford 286 mg of a yellow powder
(95%). 31P{1H} NMR (81 MHz, CDCl3, 297K): d = 54.9 and
54.8 (s, PPh2). 1H NMR (200 MHz, CDCl3, 297K): d =
7.70–6.99 (m, 136 H, HAr), 4.21 (s, 4H, S–CH2), 2.67 (m, 24H,
P–CH2), 2.42 (s, 6H, CH3). 13C NMR (75 MHz, C6D6, 297 K):
d = 193.80 (CQO), 137.95–126.92 (CAr), 118.42 and 118.07 and
116.44 (Ru–CRC–), 33.67 (CH3), 31.62 (m, |1JPC+3JPC| =
22 Hz, PCH2CH2P), 29.62 (S–CH2). IR (KBr): n (cmÀ1) =
1688 (CQO), 2057 (CRC). HR-MS FAB+ (m/z): 3320.6739
([M+] calcd: 3320.66243). Elemental analysis (%) for
trans-[AcS–(CH2)6–O–C6H4–CRC–Ru(dppe)2–CRC–C6H4–
CRC–Ru(dppe)2–CRC–C6H4–O–(CH2)6–SAc] (LCRu2LC).
With an identical procedure to SCRu2SC, 4 (193 mg,
0.084 mmol), NaPF6 (56.4 mg, 0.34 mmol), 1b (69.6 mg,
0.25 mmol) afforded 201 mg of a yellow powder (97 %).
31P{1H} NMR (121 MHz, CDCl3, 297 K): d = 55.0 (s, PPh2).
1H NMR (200 MHz, CDCl3, 297 K): d = 7.77–6.82 (m, 92 H,
3
3
H
Ar), 3.98 (t, JHH = 6 Hz, 4H, CH2–O), 2.94 (t, JHH =
6 Hz, 4H, CH2–S), 2.69 (m, 16 H, P–CH2), 2.37 (s, 6H, CH3),
1.53–1.83 (m, 16 H, CH2). 13C NMR (75 MHz, CD2Cl2,
297 K): d = 195.62 (CQO), 155.39–113.68 (CAr), 130.19
2
(quint., JPC = 15 Hz, Ru–CRC–), 117.28 and 115.46
(Ru–CRC–), 67.77 (O–CH2–), 31.2 (m, |1JPC+3JPC| =
24 Hz, PCH2CH2P), 30.46 (CH3), 29.55 (CH2), 29.28 (CH2),
28.99 (CH2), 28.57 (CH2), 25.65 (CH2). IR (KBr): n (cmÀ1) =
1690 (CQO), 2060 (CRC). HR-MS FAB+ (m/z): 2470.6074
([M+] calcd: 2470.60246). Elemental analysis (%) for
C146H138O4S2P8Ru2: C, 70.66; H, 5.67; S, 2.69 (calcd: C,
70.97; H, 5.63; S, 2.60).
C
199H170O2P12S2Ru3Á1/2CH2Cl2: C, 70.49; H, 5.19; S, 1.75
trans-[Cl(dppe)RuQCQC(H)–C6H4–CH2–SAc][TfO] (5a).
In a Schlenk tube, [(dppe)2RuCl][OTf] (825 mg, 0.75 mmol)
and 1a (290 mg, 1.52 mmol) were dissolved in CH2Cl2 (40 mL).
The solution was stirred during 2 h at room temperature. After
filtration, the solution was evaporated, then the residue was
washed with ether (4 Â 30 mL) to yield to 820 mg of a dark
green solid. 31P{1H} NMR (81 MHz, CDCl3, 297 K): d = 38.2
(s, PPh2). 1H NMR (200 MHz, CDCl3, 297 K): d = 7.51–7.05
(calcd: C, 70.95; H, 5.12; S, 1.92).
trans-[AcS–(CH2)6–O–C6H4–CRC–Ru(dppe)2–CRC–C6H4–
CRC–Ru(dppe)2–CRC-C6H4–CRC–Ru(dppe)2–CRC–
C6H4–O–(CH2)6–SAc] (LCRu3LC). With an identical proce-
dure to SCRu3SC, 5b (332 mg 0.24 mmol), NaPF6 (88 mg,
0.52 mmol), 6 (138 mg, 0.12 mmol) afforded 184 mg of
a yellow powder (63%). 31P{1H} NMR (81 MHz, CDCl3,
297 K): d = 55.0 and 54.8 (s, PPh2). 1H NMR (200 MHz,
3
(m, 40H, HAr), 6.55 (d, JHÀH = 7.8 Hz, 2H, C6H4–R), 5.64
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 2105–2113 2111

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CDCl3, 297 K): d = 7.77–6.82 (m, 136 H, HAr), 4.05
8 C. Olivier, K. Costuas, S. Choua, V. Maurel, P. Turek,
J.-Y. Saillard, D. Touchard and S. Rigaut, J. Am. Chem. Soc.,
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Chem. Soc., 2006, 128, 5859; A. Vacher, A. Benameur,
C. M. Ndiaye, D. Touchard and S. Rigaut, Organometallics, 2009,
28, 6096; S. Rigaut, J. Massue, D. Touchard, J.-L. Fillaut, S. Golhen
and P. H. Dixneuf, Angew. Chem., Int. Ed., 2002, 41, 4513.
10 Richard Feynman’s original lecture ‘‘There’s plenty of room at the
bottom’’: www.its.caltech.edu/Bfeynman.
11 A. Aviram and M. A. Ratner, Chem. Phys. Lett., 1974, 29, 277;
R. L. Carroll and C. B. Gorman, Angew. Chem., Int. Ed., 2002, 41,
437; J. A. Nitzan and M. A. Ratner, Science, 2003, 300, 1384;
R. L. McCreery, Chem. Mater., 2004, 16, 4477; C. Joachim and
M. A. Ratner, Proc. Natl. Acad. Sci. U. S. A., 2005, 102, 8801;
R. M. Metzger, J. Mater. Chem., 2008, 18, 4364; C. Joachim,
J. K. Gimzevskt and A. Aviram, Nature, 2000, 408, 541;
D. K. James and J. Tour, Chem. Mater., 2004, 15, 4423; Molecular
Nanoelectronics, ed. M. A. Reed and T. Lee, American Scientific
Publishers, Stevenson Ranch, CA, 2003.
12 (a) L. Luo, S. H. Choi and C. D. Frisbie, Chem. Mater., 2011, 23,
631; (b) S. H. Choi, B.-S. Kim and C. D. Frisbie, Science, 2008,
320, 1382; (c) A. Salomon, D. Cahen, S. Lindsay, J. Tomforh,
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3
3
(t, JHH = 8Hz, 4H, O–CH2), 2.94 (t, JHH = 8Hz, 4H,
S–CH2), 2.66 (m, 24H, P–CH2), 2.37 (s, 6H, CH3), 1.53–1.83
(m, 16H, CH2). 13C NMR (75 MHz, C6D6, 297 K): 194.09
2
(CQO), 137.81–114.03 (CAr), 130.19 (quint., JPC = 15 Hz,
Ru–CRC–), 117.28 and 115.46 (Ru–CRC–), 67.55
(O–CH2), 31.72 and 30.93 (m, |1JPC+3JPC| = 24 Hz,
PCH2CH2P), 29.96 (CH3), 29.77 (CH2), 29.37 (CH2), 28.93
(CH2), 28.55 (CH2), 25.71 (CH2). IR (KBr): n (cmÀ1) = 1687
(CQO), 2060 (CRC). HR-MS FAB+ (m/z): 3492.8181
([M+] calcd: 3392.80876).
Acknowledgements
The authors thank the CNRS, the Universite
´
de Rennes 1, and
gion
the ANR (N1ANR-09-JCJC-0025) for support, the Re
´
Bretagne for a PhD grant to E. D. P., the Algerian MESRS for
a grant to A.B. We are also grateful to Rainer Winter
(University of Konstanz) for his help with SEC measurements.
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