Molecular Engineering onto RuIIBis(1,2-diphenylphosphinoethane) Synthon: Toward an Original Organometallic Gelator

Article abstract of DOI:10.1021/acs.inorgchem.1c01488

In this article, we report the successful molecular engineering of Ru bis-acetylides that led for the first time to a gelator and more specifically in aromatic solvents. By means of a nonlinear ligand and an extended aromatic platform, the bulky Ru bis-ac

Full text of DOI:10.1021/acs.inorgchem.1c01488

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Article
Molecular Engineering onto RuII Bis(1,2-diphenylphosphinoethane)
Synthon: Toward an Original Organometallic Gelator
Olivier Galangau,* Dania Daou, Nour El Beyrouti, Elsa Caytan, Cristelle Mériadec, Franck Artzner,
and Stéphane Rigaut*
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ABSTRACT: In this article, we report the successful molecular engineering of Ru bis-
acetylides that led for the first time to a gelator and more specifically in aromatic solvents. By
means of a nonlinear ligand and an extended aromatic platform, the bulky Ru bis-acetylides
were able to self-assemble into lamellar structures as evidenced by scanning electron
microscopy (SEM) in benzene, toluene, and o- and m-xylene, which in turn induced gelation of
the solution with a critical gelation concentration of 30 mg/mL. Nuclear magnetic resonance
(NMR), variable temperature (VT)-NMR, and Fourier transform infrared (FT-IR)
spectroscopies evidenced that hydrogen bonds are mainly responsible for the self-organization.
VT-NMR and small-angle X-ray scattering (SAXS) have also suggested that the pro-ligand and
the complex stack in different ways.
logelators, rigid rod-like metal-acetylides, where the metal is
Pt(II)24−27 or Au(III),28 are efficient gelators thanks to their
flat structures and, for Pt(II) centers, their ability to provide
additional metal−metal interactions29,30 that are further
driving the supramolecular assembly. Because of their
photophysical properties, those metal-acetylide metallogels/
gelators were mainly used as light-emitting soft materials.
Alternatively, metallogels transporting electrical charges are
well desired for the development of flexible, lightweight
electronic devices, although examples have been scarcely
documented so far.31 To obtain rigid-rod conductive supra-
molecular metallogels, organometallic acetylides gelators must
combine strong supramolecular association with reversible
redox processes at low potentials.
Our group, among others, has been involved in the
chemistry of mono- and bimetallic Ru(II) bis-acetylide
complexes holding great promises for optoelectronic applica-
tions. Indeed, these compounds feature remarkable charge
transport properties in nanojunctions,32−41 on gold surfaces as
charge storage layer,42 or as ″push−pull″ chromophoric
reagents for solar cells43 and NLO applications.44−48 Recently,
we also reported Ru bis-acetylides as efficient electrochemical
switches for lanthanide emission in the NIR ranges49,50 or
INTRODUCTION
■
Supramolecular interactions are key features to obtain
(multi)functional materials with applications ranging from
optoelectronics1,2 to molecular electronics.3−5 In that regard,
molecular gels6 have received a great deal of attention in the
last decade for their appealing properties that permitted
developments of materials with high chemical sensing
abilities,7−10 remarkable charge transport properties,11 and
photochemical and electrochemical responsiveness.10,12−14
Gels can be defined as soft materials made of a liquid phase
(major component) immobilized in a 3D cross-linked network
(minor component). This network can be made of covalent
polymeric chains or prepared from the supramolecular
assembly of a low-molecular-weight compound, both being
known as the gelator. For the so-called supramolecular gels, the
gelator self-assembles thanks to a combination of weak
interactions such as van der Waals or electrostatic interactions,
hydrogen/halogen bonding, and/or π−π stacking interactions.
A gel is commonly identified by the test inversion method that
consists of looking at the ability of the soft material to support
its own weight when the vial is turned upside down. Therefore,
a gel can be interpreted as a clear sign of self-assembly
properties, whereas the lack of gelation may stem from a
limited propensity to form supramolecular polymers. Recently,
metallogels15−18 where the gelator is either a coordination or
an organometallic complex have drawn a lot of attention.
Indeed, the presence of the metal has brought about new
features such as redox responses,19 luminescence,20 or catalytic
activities.21 They have also found applications in wave-
guiding22 or for anticancer treatment.23 Among all metal-
Received: May 17, 2021
Published: July 22, 2021
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© 2021 American Chemical Society
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magnetic properties.51 However, to the best of our knowledge,
there is no example of mono- or bimetallic Ru(II) bis-acetylide
derivatives able to form supramolecular assemblies/gels, which
would widen their application field to charge transport
properties on long distances, thanks to their unique electronic
properties. This statement presumably results from the fact
that the stabilizing 1,2-dppe ancillary ligands prevent accurate
intermolecular contacts.52 Therefore, designing Ru(II) bis-
acetylide complexes able to overcome this drawback and form
supramolecular architectures accommodating their bulky
ligands is challenging.
We anticipated that placing an acetylide ligand, featuring a
simple hydrogen donating/accepting moiety in trans position
with respect to the metal center, would not be sufficient for
driving self-assembly as it is for Pt(II) bis-acetylide22
derivatives. Therefore, we selected a ligand that could trigger
the gelation of alkane solvents, while connected to a bulky
coordination sphere, such as those used in the Ln(III)
RESULTS AND DISCUSSIONS
■
Syntheses. Ru1 and Ru2 derivatives were obtained from a
multistep synthetic procedure in very good yields (Scheme 1).
Both compounds are air- and bench-stable yellow powders.
The starting compound A was converted into compound 1
through Sonogashira coupling (97%). Aniline functional
groups of 1 were further coupled to the gallic acid C
presenting three dodecyl alkyl chains, with mild conditions, to
afford the intermediate derivative 2 (91%). Finally, depro-
tection of the TMS group of 2 afforded L1 quantitatively. A
similar synthetic path was chosen for preparing L2. The
difference lies in the first step. Compound A was coupled to
derivative B featuring a TMS-protected phenyl acetylene
moiety to yield intermediate 3 in a quantitative manner. Note
that L1 and L2 are stable for months, at room temperature and
under air. Finally, Ru1 and Ru2 complexes were obtained in 83
and 82% yields, respectively, in the presence of NaPF6/Et3N.55
The temperature was maintained at 30 °C to ensure the proper
solubility of the pro-ligands. These Ru complexes were
complexes developed by Ziessel, Camerel, and Charbon-
53,54
̀
niere.
This ligand encompasses a central toluyl fragment
1
characterized with H, 13C, 31P, and FT-IR spectroscopies
connected to two amide functions that, on the basis of
crystallographic data, was found to pack in a head-to-tail
fashion with a molecular packing driven by hydrogen bonding
interactions. The toluyl fragment is essential since it prevents
the amide functions from planarizing (see Supporting
Information).
and HR-MS, and TGA proved their thermal stability up to 300
°C (Figure S40). Spectrophotometric properties of Ru1 and
Ru2 were studied in DCM (see Figure S47 and Table S4). Ru1
displays classically two main absorption bands located at 267
and 338 nm, and Ru2 presents two redshifted absorption
bands, with maxima positioned at 280 and 402 nm. On the
basis of TDDFT calculations (see Supporting Information), we
ascribed for Ru1 the transition at 338 nm to a d/π → π*
located on the dppe and the acetylide fragments, while for Ru2,
the transition at 402 nm was ascribed to a d/π → π* involving
the acetylide fragments only. We have also probed their
electrochemical behavior. Both compounds undergo a fully
reversible one-electron oxidation process at around 0.4 V vs
This article will disclose the synthesis and the physicochem-
ical properties of two original symmetrical monometallic
Ru(II) bis-acetylide complexes featuring this efficient platform
(Chart 1). It was also found that Ru2, which encompasses an
Chart 1. Molecular Structures of Ru1 and Ru2 Complexes
n
SCE in DCM (0.2 M Bu4NPF6) at room temperature as we
expected (Supporting Information). Finally, we also prepared
compound 5, which does not present the Ru-centered building
block, to investigate the importance of the molecule rod-like
shape. As a result, derivative 5 was obtained from the
homocoupling of L2 under Glaser conditions in poor yields
(17%). This low yield probably originates from the very poor
solubility of 5 in common organic solvents that prevent high
yield purification.
Gelation Properties. The gelation properties of L2, Ru1,
Ru2, and 5 studied by the inversion method are summarized in
Table 1. The pro-ligand L2 was able to form transparent gels
(Figure 1) in alkane solvents such as cyclohexane, methyl-
cyclohexane, n-dodecane, or n-heptane with a CGC (critical
gelation concentration) of 1.3 mg/mL, except for methyl-
cyclohexane (4.0 mg/mL). These values are similarly to those
found for other organic gelators possessing an analogous
structure.54 As previously reported by Ziessel et al.,56 L1 affords
turbid gels in acetone only. Therefore, extending the aromatic
platform with L2 has markedly improved the overall gelation
ability. Interestingly, gelation abilities are annihilated with
dimer compound 5 as it is not soluble in any solvents used in
this study, except in CHCl3 that was used to characterize it.
Concerning the complexes, Ru1 does not form any gels but
precipitates in cyclohexane and methylcyclohexane when
cooling down to room temperature. In aromatic solvents, the
molecule is still soluble after cooling. On the contrary, the Ru2
derivative affords turbid gels in aromatic solvents, while in
alkanes, the compound is not soluble. CGCs of approxima-
extended ligand aiming at further separating the hydrogen
bonding sites from the 1,2-dppe crowded unit and favoring
additional π−π stacking interactions, affords organogels in
aromatic solvents.
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Scheme 1. Synthetic Routes to Compounds L1, L2, Ru1 and Ru2
a
Table 1. Summary of Gelation Properties
Cy
MeCy
n-heptane
n-dodecane
benzene
toluene
o-xylene
m-xylene
L2
5
G (1.3)
NS
G (4.0)
NS
G (1.3)
NS
G (1.4)
NS
NS
NS
NS
NS
NS
NS
NS
NS
Ru1
Ru2
P
NS
P
NS
NS
NS
NS
NS
S
S
S
S
G (30)
G (20)
G (30)
G (33)
a
Numbers in bracket represent the critical gelation concentration given in mg/mL. G = gel, P = precipitate after cooling down, NS = not soluble,
and S = soluble after cooling down (no gel).
iptycene as the central bulky fragment.57 Unexpectedly, these
molecules formed gels in alkanes with CGCs ranging from 20
to 65 mg/mL. In the present case, Ru2 is the first example of its
kind providing organogels despite having such a sterically
highly demanding ancillary ligand. Furthermore, comparing
compounds 5 and Ru2 indicates that the dppe ligands play a
key role in solubilizing the organometallic molecule in
aromatic solvents. We have also measured the gel-to-solution
transition temperatures by immersing the samples in a
temperature-controlled bath. Transition temperature refers to
the temperature at which the gel (at the CGC) starts to melt
and collapses when the tube is turned upside down. Regarding
pro-ligand L2, transition temperatures of 55 °C were found in
n-heptane and n-dodecane, whereas values of 43 and 45 °C
were obtained in cyclohexane and methylcyclohexane,
respectively. As a result, gels of L2 in linear alkanes are more
robust than those in cyclic ones. Gels of Ru2 in aromatic
solvents display transition temperatures of 24 °C in toluene, 31
°C in o- and m-xylene, and 34 °C in benzene.
Figure 1. Pictures of gels from (a) Ru2 and (b) L2 derivatives. Gel-to-
solution transition temperatures are indicated at the bottom of the
figure.
tively 30 mg/mL were obtained for benzene and o- and m-
xylene, while a CGC of 20 mg/mL was measured for toluene.
When compared to the best organic gelator found in the
literature (CGC < 1 mg/mL), Ru2 gelation aptitudes are
moderate but comparable to those of other acetylide
complexes. For example, in 2011, Yang’s group reported a
series of bimetallic Pt(II) bis-acetylide complexes featuring an
Gels of Ru2 and of L2 are stable for at least 2 months in
usual laboratory conditions. Even after this period of time, the
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gelation process can be repeated at least 5−10 times with no
apparent loss of efficiency. Note that these gels do not show
any thixotropic behavior. In short, comparison between
derivatives L2, 5, Ru1, and Ru2 clearly demonstrates the
importance of (i) the 1,2-dppe ligand that brings about some
solubility and gelling ability in aromatic solvents, and (ii)
extending the aromatic surface to favor self-assembly, which
probably overcomes the steric hindrance provided by the dppe
crown, leading to more available hydrogen bonding sites and
extending the aromatic platform to offer more possibilities for
the molecules to pack thanks to π−π stacking interactions in
particular in L2 (vide infra). Comparing Ru1 and Ru2 1H NMR
spectra in CD2Cl2 where no supramolecular interactions take
place (see Supporting Information), we observed that, at room
temperature, the signal assigned to aromatic protons located
on the toluyl fragment experiences a drastic downfield shift
from Ru1 to Ru2 (from 6.80 to 7.70 ppm), while the hydrogen
atoms located on the gallate moieties are not affected. This
shift evidences the magnetic influence of the dppe crown on
these protons. Moreover, signals attributed to the methyl and
the amide protons are also similarly influenced by the dppe to a
minor extent. Therefore, it is reasonable to think that, in Ru1,
the supramolecular packing of the ligand via hydrogen bonding
and π−π stacking is prevented because of the bulkiness of the
ancillary ligand, which in turn explains why it does not afford
gels in aromatic solvent while Ru2 does (vide infra). This result
sheds light on the importance of the ligand design and on the
importance of the dppe crowding.
To further support this statement, we have transposed to our
complexes the model of Cavallo et al., originally developed for
a better understanding of catalytic activities of organometallic
complexes.58 Cavallo’s calculations provide (i) the percentage
of buried volumes, i.e., the space occupied by a ligand in the
first coordination sphere of a metal center or a putative atom,
and (ii) the corresponding topographic steric map of a ligand.
Consequently, this map provides a quantitative description of
the interaction surface between the spherical center and a
substrate. Assuming that the approach of a ″substrate″ could
be regarded as a supramolecular overlap, calculating the buried
volume (steric map) at a judiciously chosen point along the
molecular axis is highly relevant to apprehend the steric bulk of
the dppe units and the possibilities of interactions in the
present case. To achieve these calculations, we first simulated
Ru1 and Ru2 geometries with a DFT method (see Supporting
Information for more details). Then, we used these results to
calculate Cavallo’s parameters for a putative atom located at
the center of the toluyl fragment along the Ru1 and Ru2 long
molecular axis. In Ru2, the percentage of buried volume (%
Vbur) is calculated to be 0%, reflecting a free environment
available for supramolecular interactions, while in Ru1, at the
same location, %Vbur is found to be 23%, indicating that the
dppe chelate probably precludes ligand overlapping and further
supramolecular interactions.
Figure 2. SEM images of xerogels of L2 in cyclohexane, CGC = 1.3
mg/mL (a) scale bar at 5 μm and (b) scale bar at 1 μm. SEM images
of xerogels of Ru2 in benzene, CGC = 30 mg/mL (c) scale bar at 5
μm and (d) scale bar at 1 μm.
with spherical particles with diameters ranging from 200 to
1000 nm. The origin of the presence of two different types of
supramolecular objects remains elusive so far. Spherical
particles might be due to self-aggregation during the freeze-
drying step. Nevertheless, these SEM experiments prove the
capability of compound Ru2 to self-assemble into supra-
molecular ribbons. The FT-IR spectrum of these xerogels
displays the vibration of the amide CO bond at 1635 cm−1
for L2 and 1637 cm−1 for Ru2 (Figure 3). In addition, the N
Figure 3. Xerogel FT-IR spectrum of L2 in cyclohexane, CGC = 1.3
mg/mL, and of Ru2 in benzene, CGC = 30 mg/mL.
In the next sections, we now describe our further studies on
the morphologies of the gels and xerogels by scanning electron
microscopy and FT-IR.
Scanning Electron Microscopy and FT-IR Studies
(SEM). SEM was performed to study the morphology of the
corresponding xerogels (freeze-dried gels) of compounds L2
and Ru2. As observed in Figure 2, a 3D network comprising
entangled fibers was obtained for the xerogel of L2, with fiber
diameters of 100−300 nm. In contrast, Ru2 presents flat
ribbons with widths of approximatively 200−400 nm, along
H vibration from the amido moieties was found at 3153 cm−1
for L2 and 3230 cm−1 for Ru2. These values are characteristic
of hydrogen-bonded molecules and are close to values found
for a very similar molecular skeleton.54
NMR Studies of Gelation. To get more insight into the
supramolecular processes, the gel formation was monitored by
1H variable temperature NMR (VT-NMR) studies in C6D12
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a
1
Scheme 2. Partial H VT-NMR Monitoring of Ru2 in C6D6 (c = 30 mg/mL)
a
Inset shows 31P{1H}VT-NMR monitoring recorded in the same conditions. Lines are used as guide for the eye. Red line = amide protons, green
line = methyl signal, and purple line = 1,2-dppe signals.
1
for L2 and C6D6 for Ru2. Starting with compound L2 (see
Supporting Information), the broad signal located at 8.3 ppm
assigned to amide group protons experiences a downfield shift
(+0.61 ppm) as the temperature decreases from 340 to 320 K.
This is a clear evidence of the involvement of the hydrogen
bonds into the supramolecular process as indicated in the
xerogel with IR spectroscopy. Interestingly, aromatic signals
experience an upfield shift as well as the methyl protons’ signal
located at 2.00 ppm (−0.13 ppm). Finally, the alkynyl proton
exhibits no shift, which leads us to think that this part of the
molecule is not involved in the supramolecular packing.
Additional 2D ROESY experiment performed at 325 K features
a cross-correlation between the alkynyl proton and some
protons from the aliphatic chains (Figure S29), which proves
that these two groups of atoms are spatially close during the
self-assembly process. These observations are consistent with a
head-to-tail supramolecular assembly as previously suggested
by Ziessel et al. on an analogous system (see Supporting
Information).54 As far as the Ru2 derivative is concerned, we
suggested by qualitative observations. Regarding the H NMR
spectrum, the broad singlet signal located at 7.45 ppm and
assigned to amide protons experiences a significant downfield
shift from 340 to 300 K (+0.55 ppm). This is in line with
molecules interacting through hydrogen bonds, presumably
between their amide groups, as for L2. Importantly, the singlet
signal located at 2.20 ppm (methyl protons) also experiences a
downfield shift. This is in stark contrast with what was
observed on ligand L2 and might suggest, at this stage, that Ru2
does not pack the same way as L2 does. However, the choice of
solvent deeply matters in the context of supramolecular
chemistry, and therefore, the comparison between L2 and Ru2
may not be so straightforward.59 Interestingly, multiplet signals
due to the dppe aromatic protons do not shift with
temperature, indicating that the dppe is not involved in the
supramolecular process, as we anticipated. Additional 2D
NOESY and 2D ROESY performed at 315 K exhibit cross-
correlations indicating several dipolar couplings between
protons of the toluyl fragment, the amido groups, and the
fatty chains (Figures S30 and S31). These through-space
couplings support the existence of supramolecular contacts
involving the acetylide ligands. Further variable temperature
DOSY-NMR (Figure S29) was conducted in C6D6 at the CGC
to measure the gel-to-solution transition temperature. The
molecular diffusion coefficient decreased with temperature
before reaching a plateau at 32 °C, meaning that the gel state
was obtained. This value is in good agreement with the one
measured previously (Figure 1).
1
have conducted H and 31P VT-NMR experiments in C6D6 at
the CGC (Scheme 2). First, the 31P{1H} experiment displays
one singlet signal located at approx. 53.5 ppm at 340 K, a value
that is characteristic of a Ru(II) trans-bis-acetylide complex. By
slowly cooling down the sample to 295 K, the singlet signal
undergoes a slight shift and vanishes because of gelation at 300
K. This singlet signal reappears when the sample is warmed
above the gelation temperature. We repeated this experiment
at least four times and showed great reproducibility with no
obvious degradation. Therefore, we can safely conclude that
Ru2 is chemically stable in that temperature range, as already
To sum up, experiments that combined FT-IR with NMR
and VT-NMR have clearly established that hydrogen bonds are
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involved in the construction of the supramolecular assemblies.
On one hand, L2 seems to behave as reported by Ziessel et al.,
with molecules packing in a head-to-tail fashion and rejecting
the alkynyl protons out of the structure. On the other hand,
whereas the Ru2 compound also exhibits hydrogen bonding
that is central for the assembly (downfield shift of the amide
proton signal), the methyl signal also experiences a downfield
shift that is inconsistent with a head-to-tail supramolecular
packing. Eventually, VT-NMR, 2D NOESY, and 2D ROESY
clearly evidence that dppe is not involved in the supramolecular
process.
0.344 and 0.69 Å−1 corresponding to long-range order with a
lamellar repeat distance aL of 18.2 Å (Supporting Information,
Figure 5). An additional broad scattering is observed at 0.15
Å
−1 indicating a short-range order interdistance bL of 42 5 Å.
This suggests a lamellocolumnar organization. In this
hypothesis, the columnar cross section is SL = aL × bL = 760
Å2. These arrangements and surface are close to those of the
parent system54 and confirm the column formation tendency
observed by NMR and FT-IR. Note that the orientation of the
diamido backbone can be either in-plane or perpendicular to
the layer. However, this can be clarified by noting that the
aromatic volume ratio is between 25 and 30%. This imposes
the mean thickness of the aromatic part in the lamellar
structure to be thinner than 5.5 Å, which is incompatible with a
perpendicular orientation. The in-plane orientation is compat-
ible with observed H-bonds and the head-to-tail packing
hypothesis. Thus, the hierarchical structure of the gel is
consequently formed by large fibers that are made of columns
with a head-to-tail packing organized in layers by means of
chain interdigitation.
Small-Angle X-ray Scattering (SAXS). To get a better
insight into the supramolecular architectures of both gels, we
performed small-angle X-ray scattering experiments. The X-ray
scattering of the ligand L2 (Figure 4) exhibits two peaks at
The X-ray scattering of Ru2 (Figure 4) exhibits a well-
defined set of lamellar peaks at 0.158, 0.32, 0.48, and 0.65 Å−1
corresponding to a repeat distance aRu of 39.2 Å. The length of
the aromatic-ethenyl-Ru rigid part is about 33 Å. This is
compatible with a perpendicular orientation to the layers.
Interestingly, the amide backbone is parallel to the layer and
therefore perpendicular to the mean plane containing the
acetylide scaffold. In other words, Ru2 forms lateral
intermolecular hydrogen bonds leading to layers of molecules
showing a segregation between the aliphatic part and the
aromatic part. Thanks to chain interdigitations, the layers
assemble together affording large ribbons (Figure 5)
responsible for the gelation. In particular, aromatic solvent
molecules might be confined within the layers, therefore
contributing to the overall solvent immobilization. Such a
result echoes with the fact that the Ru2 gels are weak, are
fragile, and feature moderate gel-to-sol transition temperatures.
Overall, SAXS confirms that L2 and Ru2 present different
packing as already suggested by the VT-NMR experiments.
Figure 4. SAXS diffractogram of L2 and Ru2 collected in gels at their
respective CGC. Patterns are shifted for clarity. Dotted arrows
correspond to lamellar peaks. The solid line indicates a lateral order
within the layers.
Figure 5. Schematic of the internal structure of (a) L2 fibers and (b) Ru2 ribbons according to the SAXS data.
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monochromatic Cu Kα radiation is of λ = 1.541 Å. The diffraction
patterns were therefore recorded for reciprocal spacing q = 4π × sinθ/
λ in a range of repetitive distances from 0.015 Å−1 (418 Å) to 1.77
Å−1 (8 Å). Images were transformed to graphics using a home-
developed program.
CONCLUSIONS
■
To conclude, we have successfully synthetized the first example
of a Ru(II) bis-acetylide complex showing supramolecular
capabilities. By means of a rational molecular engineering that
consists of (i) placing hydrogen bonding accepting/donating
groups out of the molecule’s long axis and (ii) extending the
ligand platform to decrease the steric influence of the dppe
crown, this complex was able to form ribbons in aromatic
solvents, which in turn induced gelation of the solution. In
particular, NMR, VT-NMR, and FT-IR spectroscopies have
evidenced that hydrogen bonds are mainly responsible for the
self-organization. VT-NMR and SAXS have also suggested that
both the pro-ligand and the complex self-assemble thanks to
hydrogen bonding interactions. While L2 packs in a head-to-
tail fashion, Ru2 forms lateral hydrogen bonding with a
segregation between the aliphatic and the aromatic parts. We
are currently investigating the self-assembly mechanism and
the necessity for the complex to be symmetrical to generate
supramolecular packing. We believe that these results open the
door to new opportunities for redox active Ru bis-acetylide
compounds and will encourage the development of new parent
complexes featuring improved gelation efficiencies.
SYNTHESES
■
Compound 1. A dried Schlenk tube was charged with
compound A (0.200 g, 0.8 mmol, 1 eq.), PdCl2(PPh3)2 (0.085
g, 5 mol %), and CuI (0.023 g, 5 mol %) under argon flow.
Then, distilled Et3N (12 mL) was added followed by dry THF
(12 mL). To this mixture was added the excess of neat TMSA
(500 μL, 5 mmol, 2 eq.), and the mixture was refluxed for 24 h.
The crude was allowed to cool to room temperature and was
diluted with aq. NH4Cl saturated solution. The aqueous layer
was extracted with EtOAc several times. The organics were
dried over Na2SO4 and filtered, and the solvents were
removed. The crude mixture was purified by flash column
chromatography (silica, DCM/EtOH 0 to 1.2%) to afford 512
1
mg of the expected compound 1 (yield 97%). H NMR (400
MHz, CDCl3): δ = 6.33 (s, 2HAr), 3.53 (broad singlet,
4Hamine), 1.95 (s, 3Hmethyl), 0.22 (s, 9HTMS); 13C NMR (100
MHz, CDCl3): δ = 144.84, 120.92, 110.25, 108.47, 105.74,
92.08, 10.31, 0.02 (CTMS). HRMS (ESI): m/z 219.1312 calcd
for C12H19N2Si [M + H+]; found: 219.1312.
EXPERIMENTAL SECTION
■
General Information. Chemicals and solvents (HPLC, spectro-
scopic grade) were purchased from Merck-Sigma Aldrich, Acros
Organics, Alfa Aesar, and Fisher Scientific and were used without any
further treatment. Anhydrous (HPLC) solvents were obtained from a
MBraun SPS-800 drying system. Dry THF was obtained after
distillation on Na/benzophenone. Dry diisopropylamine (DIPA), dry
triethylamine (TEA), and dry DMF were obtained after distillation on
CaH2 and kept in the dark on molecular sieves. All reactions were
carried out under an argon atmosphere using Schlenk techniques,
unless otherwise stated. Schlenk tubes were dried under vacuum using
a heat gun. TLC analyses were achieved on silica gel bought from
Fluka (silica gel matrix containing a fluorescent indicator at 254 nm).
Column chromatography was performed on silica gel from Acros
Organics (pore size of 60 Å, particle size of 40−63 μm), unless
Compound Ru1. A dried Schlenk flask was charged with cis-
RuCl2(dppe)2 (0.050 g, 0.05 mmol, 1 eq.), compound L1
(0.165 g, 0.11 mmol, 2.2 eq.), and NaPF6 (0.052 g, 0.31 mmol,
6 eq.) under argon flow. The tube was evacuated (30 min) and
backfilled with argon. Then, a solution of distilled Et3N (417
μL, 3 mmol, 60 eq.) in dry DCM (16 mL) was added with a
syringe. The reaction mixture was stirred at 30 °C during 4
days. 31P{1H} (no lock procedure) NMR monitoring of the
reaction indicated only one singlet signal at around 53 ppm.
The reaction mixture was diluted with DCM (10 mL) and
washed with water (3 × 10 mL). The organic layer was
collected, dried on Na2SO4, and filtered, and the solvent was
removed. The crude was taken up in 10 mL of DCM and
precipitated by dropwise addition of 10 mL of MeOH. The
yellow precipitate was filtered off under air and dried to afford
the corresponding Ru1 compound (m = 0.164 g, yield 83%).
1
otherwise stated. H, 13C, and 31P-NMR spectra were recorded on a
Bruker Avance III (400 MHz) and Bruker AMX-3300 (300 MHz) at
303 K. Relevant compounds were also characterized by 2D NMR
using HSQC/HMQC, COSY H−1H, and HMBC sequences. VT-
1
NMR was recorded on a Bruker Ascend 500 MHz Av III HD.
Deuterated solvents were bought from Euriso-top. Infrared spectra
(KBr) were acquired on an FT-IR BRUKER EQUINOX 55
spectrophotometer. HR-MS spectra were obtained from the Centre
1H NMR (400 MHz, CD2Cl2): δ = 7.51 (m, 20H Hdppe
+
3
Hamide), 7.49 (t, 16H, JHH = 7.6 Hz, Hdppe), 7.13−7.17 (m,
16H, HAr + Hdppe), 6.81 (s, 4H, Htol), 4.08 (dt, 24H, 3JHH = 6.5
Hz, Halkyl), 2.66 (br. s, 8H, CH2dppe), 2.17 (s, 6H, HMe), 1.88−
1.71 (m, 28H, Hchain), 1.54 (m, Hchain), 1.28 (br. s, 205H,
́
Regional de Mesures Physiques de l’Ouest (CRMPO). Intermediate
A was obtained through an adapted procedure from the literature (see
Supporting Information). Precursors B and C were synthetized as
reported in the literature (see Supporting Information for reference).
Thermogravimetric Analyses. TGA curves were recorded on a
TGA-DSC 1 STAR System under a nitrogen atmosphere.
Electrochemical Measurements. 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
carbon disk and decamethylferrocene was the internal reference.
Scanning Electron Microscopy (SEM). Metallization by Au/Pd.
Scanning electron microscopy (SEM) of xerogels was evaluated using
the JEOL IT 300 scanning electron microscope. Samples were
collected and deposited on a Teflon plot. Each sample was examined
using a voltage of 5 or 10 kV. Images were analyzed by the SMileView
software.
H
chain), 0.88 (m, 36H, MeChain); 13C NMR (75 MHz, CD2Cl2):
δ = 166.09, 153.75, 141.68, 141.68, 137.46 (quint, J = 10.2
Hz), 136.27, 134.61, 130.43, 129.09, 127.57, 125.24, 123.13,
1
3
116.07, 73.93, 69.82, 32.39, 31.85 (m, JP,C + JP,C = 24 Hz,
P(CH2)2P), 30.81, 30.21−29.81 (br. m.), 26.59, 23.14, 23.12,
14.32, 13.13. 31P{1H} NMR (162 MHz, CD2Cl2): δ = 53.17.
HRMS (ESI): m/z 3814.6316 calcd for C242H370N4O16P4102Ru
[M+.]; found 3814.6298. IR (cm−1): 3255 (νN−H), 2912, 2851
(νC−H), 2051 (νC ≡ C), 1639 (νCO), 1582 (νCC). λmax
(solvent, ε): 338 nm (DCM, 38000 L mol−1 cm−1).
Compound 3. A dried Schlenk tube was charged with
compound A (0.200 g, 0.8 mmol, 1 eq.), compound B (0.208
g, 1.0 mmol, 1.3 eq.), PdCl2(PPh3)2 (0.028 g, 5 mol %), and
CuI (0.007 g, 5 mol %) under argon flow. Dry THF (4 mL)
and dry DIPA (4 mL) were added by a syringe. The mixture
darkened. The dark solution was refluxed (65 °C) for 24 h.
The crude was diluted with saturated aq. NH4Cl solution and
Small-Angle X-ray Scattering (SAXS). Organogel and xerogel
samples were prepared inside capillaries. SAXS experiments were
performed using X-ray patterns collected with a Pilatus 300k (Dectris,
Grenoble, France) mounted on a GeniX 3D (Xenocs, Sassenage,
France) microsource X-ray generator operating at 30 W. The
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Article
extracted with Et2O several times. The organics were
combined, dried over MgSO4, and filtered, and the solvents
were removed. Purification by column chromatography (silica,
DCM/EtOAc mixture) afforded the desired compound 3 (m =
0.230 g, yield 90%).1H NMR (400 MHz, CDCl3): δ = 7.42 (s,
4H, H10/11), 6.38 (s, 2H, H7), 3.59 (broad singlet, 4H, Hamine),
1.97 (s, 3H, H1), 0.26 (s, 9H, HTMS); 13C NMR (100 MHz,
CDCl3): δ = 145.09 (C12), 131.78 (C11b), 131.28 (C11a),
123.69 (C10), 122.47 (C9), 120.77 (C8), 109.73 (C7), 108.35
(C6), 104.73 (C5), 95.98 (C4), 91.99 (C3), 87.35 (C2), 10.33
(C1), −0.09 (CTMS). HRMS (ESI): m/z 341.1445 calcd for
C20H22N2Si Na [M + Na+]; found: 341.1445.
added, and the suspension was stirred 4−5 h. The mixture was
partitioned between water and DCM. The aqueous layer was
extracted several times with DCM. The organic phase was
dried on MgSO4 and filtered, and the solvents were removed to
afford a light yellowish powder with enough purity to be used
1
for the next step (0.635 g, yield 99%). H NMR (300 MHz,
Compound 4. A dried Schlenk tube was charged with
compound 3 (0.164 g, 0.52 mmol, 1 eq.), compound C (0.870
CDCl3): δ = 7.98 (s, 2H, Hamide), 7.59 (s, 2H, H18), 7.41 (d,
2H, 3JHH = 8.2 Hz, H21), 7.33 (d, 2H, 3JHH = 8.2 Hz, H21), 7.14
(s, 4H, H14), 4.02 (m, 12H, H8/9), 3.15 (s, 1H, Halkyne), 2.17 (s,
3H, H1), 1.80 (m, 12H, H6), 1.47−1.27 (m, 108H, H4/5), 0.88
(m, 18H, H2); 13C NMR (75 MHz, CDCl3): δ = 165.96 (C25),
153.26 (C24), 141.70 (C23), 136.40 (C22), 131.99 (C21b),
131.39 (C21a), 128.94 (C20), 127.69 (C19), 125.51 (C18),
123.45 (C17), 121.93 (C16), 121.08 (C15), 105.96 (C14), 90.51
(C13), 89.23 (C12), 83.20 (C11), 78.88 (C10), 73.57 (C9), 69.40
(C8), 31.92 (C7), 30.36 (C6), 29.76 (C5), 29.66 (C5), 29.45
(C5), 29.37 (C5), 29.36 (C5), 26.12 (C4), 22.68 (C3), 14.10
(C2), 13.38 (C1). HRMS (ESI): m/z 1582.2536 calcd for
C
103H166N2O8Na [M + Na+]; found: 1582.2543. IR (cm−1):
3442 (νN−H), 3288 (νCC−H), 2916 (νC−H), 2852 (νC−H), 2107
(νC ≡ C), 1635 (νCO), 1583 (νCC).
Compound 5. A round-bottom flask equipped with a
magnetic stirring bar was charged with compound L2 (0.448 g,
1 mmol, 1 eq.), anhydrous CuCl2 (0.004 g, 0.0287 mmol 0.1
eq.), and THF (6 mL). Neat DBU was added dropwise (0.051
mL, 0.34 mmol, 1.2 eq.). The mixture was refluxed over 1 day
with no precaution to remove air. The reaction mixture was
taken to dryness. Purification by column chromatography
(Florosil, PE/CHCl3 (9/1, v/v) to CHCl3) followed by
precipitation in a mixture of CHCl3 and MeOH afforded the
g, 1.3 mmol, 2.5 eq.), EDC-HCl (0.248 g, 1.3 mmol, 2.5 eq.),
and DMAP (0.157 g, 1.3 mmol, 2.5 eq.) under argon flow. Dry
DCM (3.5 mL) was added via a syringe. The brownish
solution was then warmed at 30 °C over 3 days. The crude was
diluted with DCM and washed with water. The organic phase
was collected, dried on Na2SO4, and filtered. The solvent was
removed. Purification by column chromatography (silica,
DCM/EtOAc 100%/0% to 98%/2%) afforded the desired
1
1
compound (m = 0.671 g, yield 80%). H NMR (400 MHz,
pure compound 5 (m = 0.150 g, yield 17%). H NMR (400
CDCl3): δ = 7.74 (s, 2H16), 7.65 (br. s, 2H, Hamide), 7.42 (s,
4H, H18), 7.09 (s, 4H,H14), 4.04 (m, 12H, H8), 2.25 (s, 3H,
H1), 1.83 (m, 12H, H2−7), 1.43−1.23 (m, 108H, H2−7), 0.88
(m, 18H, H2−7), 0.25 (s, 9H, HTMS); 13C NMR (75 MHz,
CDCl3): δ = 165.94 (C23), 153.28 (C22), 141.77 (C21), 139.67
(C20), 136.43 (C19), 131.83 (C18b), 131.32 (C18a), 128.99
(C17), 125.42 (C16), 123.05 (C15), 123.00 (C14), 106.02 (C13),
104.61 (C12), 96.25 (C11), 90.45 (C10), 89.45 (C8/9), 73.59
(C8/9), 69.44 (C7), 31.92 (C6), 30.36 (C5), 29.75 (C5), 29.71
(C5), 29.66 (C5), 29.61 (C5), 29.44 (C5), 29.36 (C5), 26.11
(C4), 22.68 (C3), 14.09 (C2), 13.36 (C1), −0.10 (CTMS).
HRMS (MALDI-DCTB): m/z 1654.293 calcd for
MHz, CDCl3): δ = 7.90 (s, 4H, Hamide), 7.64 (s, 4H, HAr tol),
7.44 (d, 4H, 3JHH = 8.3 Hz, HAr acetylene), 7.37 (d, 4H, 3JHH = 8.3
Hz, HAr acetylene), 7.12 (s, 8H, HAr side), 4.02 (m, 24H,
H
Omethylene), 2.20 (s, 6H, HMethyl), 1.81 (m, 24H, Hchain),
1.47−1.26 (m, 216H, Hchain), 0.88 (m, 36H, Hchain); 13C NMR
(75 MHz, CDCl3): δ = 166.07, 153.24, 141.73, 136.40, 132.32,
131.48, 128.91, 128.13, 125.83, 123.90, 121.45, 121.05, 106.06,
91.28, 89.35, 82.01, 75.72, 73.56, 69.41, 31.82, 30.38, 29.76,
29.67, 29.47, 29.37, 26.13, 22.68, 14.08, 13.36. HRMS (ESI):
m/z 3139.5024 calcd for C206H330N4O16Na [M + Na+]; found:
3139.5007. IR (cm−1): 3181 (νN‑H), 2916 (νC−H), 2054
(νC−H), 1636 (νCO), 1583 (νCC).
C
106H174N2O8SiNa [M + Na+]; found: 1654.282. IR (cm−1):
Compound Ru2. A dried Schlenk flask was charged with cis-
RuCl2(dppe)2 (0.121 g, 0.13 mmol, 1 eq.), compound L2
(0.400 g, 0.26 mmol, 2.05 eq.), and NaPF6 (0.122 g, 0.73
mmol, 5.8 eq.) under argon flow. The tube was evacuated and
backfilled with argon. Then, a solution of distilled Et3N in dry
DCM (16 mL) was added. Finally, the reaction mixture was
warmed at 30 °C during 4 days. 31P{1H} (no lock procedure)
NMR monitoring indicated only one singlet signal at 52.8
3177 (νN−H), 2917 (νC−H), 2850 (νC−H), 2109 (νC≡C), 1635
(νCO), 1580 (νCC).
Compound L2. A round-bottom flask equipped with a
magnetic stirring bar was charged with compound 4 (0.671 g,
0.41 mmol, 1 eq.). The compound was dissolved in a 1/1 (v/
v) DCM and MeOH (total volume of 30 mL) at room
temperature. Then, K2CO3 (2.552 g, 18.5 mmol, 45 eq.) was
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Article
Notes
ppm. The reaction was stopped by adding 20 mL of MeOH
over 20 min. The compound was filtered off. The powder was
taken up in DCM (20 mL) and precipitated with MeOH (8
mL) to afford pure compound Ru2 as a yellow powder (m =
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
1
0.412 g, yield 82%). H NMR (400 MHz, CD2Cl2): δ = 7.74
The authors thank the Université de Rennes 1 and the CNRS
for the support. The authors are grateful to Dr. Camerel for the
fruitful discussions about the gel formation. This work was
granted access to the computing resources of CINES
(Montpellier, allocation 2019-A0060810728 and 2020-
AP010811752 awarded by GENCI). The authors also thank
F. Gouttefangeas and L. Joanny from the CMEBA (Centre de
(s, 4H, Hamide), 7.73 (s, 4H, Htol), 7.49 (m, 16H, Hdppe), 7.30
(d, 4H, 3JHH = 8.3 Hz, HAr acetylene), 7.20 (s, 8H, 3JHH = 7.5 Hz,
H
dppe), 6.97 (t, 16H, 3JHH = 7.7 Hz, Hdppe), 6.72 (d, 4H, 3JHH
=
8.4 Hz, HAr acetylene), 4.04 (dt, 24H, 3JHH = 6.6 Hz, HOmethylene),
2.66 (br. s, 8H, Hdppe), 2.25 (s, 6H, HMe), 1.88−1.71 (m, 28H,
H
aliphatic), 1.54 (m, Haliphatic), 1.28 (br. s, 205H, Haliphatic), 0.88
(m, 36H, Haliphatic); 13C NMR (75 MHz, CD2Cl2): δ = 165.91,
153.27, 141.47, 137.17, 137.00, 136.87, 136.69, 134.10, 130.89,
130.76, 129.99, 129.83, 129.23, 128.74, 127.77, 125.29, 121.72,
117.63, 116.58, 105.82, 90.93, 88.53, 73.49, 69.37, 31.94, 31.38
̀
Microscopie Electronique a Balayage et microAnalyse, Rennes)
for assistance in recording SEM images.
1
3
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CD2Cl2): δ = 52.89. HRMS (ESI): m/z 1338.2312 calcd for
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ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01488.
Precursor synthetic procedures; NMR spectra of L2, 5,
Ru1, and Ru2; comparative NMR studies of Ru1 and Ru2
in CD2Cl2; VT-NMR monitoring for compounds L2 and
Ru2; gel formation procedure and corresponding
summary of the gel properties; SEM images; absorption
spectrum of Ru1 and Ru2; CV of Ru1 and Ru2; and DFT
and TDDFT calculations for Ru1 and Ru2 (PDF)
AUTHOR INFORMATION
■
Corresponding Authors
(10) Yang, X.; Zhang, G.; Zhang, D. Stimuli responsive gels based on
low molecular weight gelators. J. Mater. Chem. 2012, 22, 38−50.
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Samori, P. Supramolecular Self-Assembly in a Sub-micrometer
Electrodic Cavity: Fabrication of Heat-Reversible pi-Gel Memristor.
J. Am. Chem. Soc. 2017, 139, 14406−14411.
Olivier Galangau − Univ Rennes, CNRS, ISCR (Institut des
Sciences Chimiques de Rennes)-UMR 6226, Rennes F-35000,
France; Email: olivier.galangau@univ-rennes1.fr
Stéphane Rigaut − Univ Rennes, CNRS, ISCR (Institut des
Sciences Chimiques de Rennes)-UMR 6226, Rennes F-35000,
France; orcid.org/0000-0001-7001-9039;
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Commun. 2016, 52, 8196−8206.
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Dania Daou − Univ Rennes, CNRS, ISCR (Institut des
Sciences Chimiques de Rennes)-UMR 6226, Rennes F-35000,
France
Nour El Beyrouti − Univ Rennes, CNRS, ISCR (Institut des
Sciences Chimiques de Rennes)-UMR 6226, Rennes F-35000,
France
Elsa Caytan − Univ Rennes, CNRS, ISCR (Institut des
Sciences Chimiques de Rennes)-UMR 6226, Rennes F-35000,
France; orcid.org/0000-0003-0490-3074
Cristelle Mériadec − Univ Rennes, CNRS, IPR (Institut de
Physique de Rennes)-UMR 6251, Rennes F-35000, France
Franck Artzner − Univ Rennes, CNRS, IPR (Institut de
Physique de Rennes)-UMR 6251, Rennes F-35000, France
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