2D and 3D Ruthenium Nanoparticle Covalent Assemblies for Phenyl Acetylene Hydrogenation

Article abstract of DOI:10.1002/ejic.202000698

The bottom-up covalent assembly of metallic nanoparticles (NP) represents one of the innovative tools in nanotechnology to build functional heterostructures, with the resulting assemblies showing superior collective properties over the individual NP for a broad range of applications. The ability to control the dimensionality of the assembly is one of the major challenges in designing and understanding these advanced materials. Here, two new organic linkers were used as building blocks in order to guide the organization of Ru NP into two- or three-dimensional covalent assemblies. The use of a hexa-adduct functionalized C₆₀ leads to the formation of 3D networks of 2.2 nm Ru NP presenting an interparticle distance of 3.0 nm, and the use of a planar carboxylic acid triphenylene derivative allows the synthesis of 2D networks of 1.9 nm Ru NP with an interparticle distance of 3.1 nm. The Ru NP networks were found to be active catalysts for the selective hydrogenation of phenylacetylene, reaching good selectivity toward styrene. Overall, we demonstrated that catalyst performances are significantly affected by the dimensionality (2D vs. 3D) of the heterostructures, which can be rationalize based on confinement effects.

Full text of DOI:10.1002/ejic.202000698

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doi.org/10.1002/ejic.202000698
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Nanoparticle Macrostructures
2D and 3D Ruthenium Nanoparticle Covalent Assemblies for
Phenyl Acetylene Hydrogenation
Yuanyuan Min,[a] Faqiang Leng,[a] Bruno F. Machado,[b] Pierre Lecante,[c] Pierre. Roblin,[d]
Hervé Martinez,[e] Thomas Theussl,[f] Alberto Casu,[g] Andrea Falqui,[g] María Barcenilla,[h]
Silverio Coco,[h] Beatriz María Illescas Martínez,[i,j] Nazario Martin,[i,j] M. Rosa Axet,*[a] and
Philippe Serp*[a]
Abstract: The bottom-up covalent assembly of metallic nanopar- tionalized C60 leads to the formation of 3D networks of 2.2 nm
ticles (NP) represents one of the innovative tools in nanotechnol- Ru NP presenting an interparticle distance of 3.0 nm, and the
ogy to build functional heterostructures, with the resulting use of a planar carboxylic acid triphenylene derivative allows the
assemblies showing superior collective properties over the indi- synthesis of 2D networks of 1.9 nm Ru NP with an interparticle
vidual NP for a broad range of applications. The ability to control distance of 3.1 nm. The Ru NP networks were found to be active
the dimensionality of the assembly is one of the major challen- catalysts for the selective hydrogenation of phenylacetylene,
ges in designing and understanding these advanced materials. reaching good selectivity toward styrene. Overall, we demon-
Here, two new organic linkers were used as building blocks in strated that catalyst performances are significantly affected by
order to guide the organization of Ru NP into two- or three- the dimensionality (2D vs. 3D) of the heterostructures, which can
dimensional covalent assemblies. The use of a hexa-adduct func- be rationalize based on confinement effects.
1. Introduction
trial development. In nature, the chemical transformation proc-
esses often occur in molecularly crowded and/or confined envi-
ronment with well-designed limited spaces such as nanometric-
sized enzymes.[1] With the development of nanosciences and
nanotechnology, various nanoreactors, both organic or inor-
ganic,[2] have been designed for catalytic applications;[3] provid-
ing constrained spaces isolated from the surrounding environ-
ment. In heterogeneous catalysis, confinement effects (CE) can
greatly influence catalytic performances.[4] The CE can be either
physical or chemical, and are induced by the reduction of the
dimensions of the spaces in which a chemical reaction takes
places. The physical effects can lead to shape-selectivity,[5] im-
pact the nanofluidics and mass transport,[6] phase separation,
Catalysts are essential in the majority of industrial chemical
transformation processes, and the optimization of catalyst per-
formances is a sine qua non condition for a sustainable indus-
[a] Dr. Y. Min, Dr. F. Leng, Dr. M. Rosa Axet, Prof. Dr. P. Serp
CNRS, LCC (Laboratoire de Chimie de Coordination),
INPT, 205 route de Narbonne, 31077 Toulouse Cedex 4, France
E-mail: rosa.axet@lcc-toulouse.fr, philippe.serp@ensiacet.fr
https://www.lcc-toulouse.fr/article447.html?lang=fr
Twitter: Laboratoire de chimie de coordination @LCC_CNRS
[b] Dr. B. F. Machado
LSRE-LCM, Chemical Engineering Department, Faculty of Engineering, University of Porto,
Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
[c] Dr. P. Lecante
Centre d'élaboration des matériaux et d'études structurales UPR CNRS 8011,
29 Rue Jeanne-Marvig, BP 4347, 31055 Toulouse, France
[d] Dr. P. Roblin
Laboratoire de Génie Chimique and Fédération de Recherche FERMAT,
4 allée Emile Monso, 31030 Toulouse, France
[e] Prof. Dr. H. Martinez
Université de Pau et des Pays de l'Adour, 64053 Pau, France
[f] Dr. T. Theussl
King Abdullah University of Science and Technology (KAUST),
Visualization Core Lab, 23955-6900 Thuwal, Saudi Arabia
[g] Dr. A. Casu, Dr. A. Falqui
King Abdullah University of Science and Technology (KAUST), Biological and Environmental
Sciences and Engineering (BESE) Division, NABLA Lab, 23955-6900 Thuwal, Saudi Arabia
[h] Dr. M. Barcenilla, Prof. Dr. S. Coco
IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid,
47071 Valladolid, Spain
[i] Prof. Dr. B. M. I. Martínez, Prof. Dr. N. Martin
Departamento Química Orgánica, Facultad C. C. Químicas, Universidad Complutense de
Madrid, Av. Complutense s/n, 28040 Madrid, Spain
Scheme 1. Representation of different nanoreactors with a confined metallic
nanoparticle and a reactant molecule (here phenyl acetylene): a) a metallic
cluster confined in a zeolite cage; b) metallic clusters confined in a carbon
nanotube; c) metallic clusters covered by a graphene overlayer; and d) cova-
lent network of metallic clusters where the black lines represent the organic
linkers.
[j] Prof. Dr. B. M. I. Martínez, Prof. Dr. N. Martin
IMDEA-Nanociencia, C/Faraday 9, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain
Supporting information and ORCID(s) from the author(s) for this article are available
on the WWW under https://doi.org/10.1002/ejic.202000698.
Part of the Supported Catalysts Special Collection.
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phase equilibria[7] and transformation,[8] or to significant pres- their use in catalysis.[15a,15b,20] Some studies have already evi-
sure enhancement.[9] The chemical effects are related to modifi- denced that NP covalent assembly show better catalytic per-
cations of the electronic interactions between the catalytic formances, and in some cases higher stability than isolated
phase and the surrounding material, which alter the adsorption NP.[20,21] Another interesting aspect of these assemblies is the
energetics, influencing the formation and breaking of chemical possibility of controlling the interparticle distance via the
bonds. All these effects can directly contribute to enhancement molecular chemical nature and chain length of the ligand,[15a,22]
of activity/selectivity and catalyst stabilization. CE have been and possibly the CE. We have recently demonstrated in the case
studied in 0D nanoreactors such as zeolites[10] (Scheme 1a) or of 3D Ru NP networks linked with polymantane ligands that it
MOF,[11] 1D nanoreactors such as carbon nanotubes was possible to: i) obtain NP with similar size (1.6–1.8 nm) for a
(Scheme 1b)[12] or covalent organic frameworks,[13] and more given metal loading whatever the nature of the ligand (diacid
recently, under the layers of 2D materials such as graphene or diamine); ii) control the electronic effects by means of the
(Scheme 1c).[14] In all these systems the active phase, often a chemical nature of the ligand (acid vs. amine); and iii) control
transition metal nanoparticle (NP), is confined in a cavity com- the interparticle distance via the size of the ligand.[15a] We also
posed of a second material. Another type of material that could demonstrated that catalyst activity and selectivity in phenyl-
offer interesting perspectives to study CE consists in covalent acetylene hydrogenation are both significantly affected by
assemblies of metallic NP (Scheme 1d).[15] In these structures, Ru NP interparticle distance and therefore by CE.
the organic linker (or ligand) plays a fundamental role on con-
structing the NP network and defining NP chemical environ-
ment.[16] In that case, the reactant environment is significantly
different since it is composed of an important number of cata-
lytically active NP covalently linked by an organic molecule. The
interparticle coupling effect has been demonstrated to signifi-
cantly influence the optical properties of NP,[17] and is also able
to affect their catalytic properties.[18]
In continuation of our ongoing research in the development
of Ru NP covalent assemblies for catalysis,[15a,15b] the present
work aims at producing 2D and 3D Ru NP networks via a ra-
tional choice of new organic linkers, and to study their catalytic
performances for phenylacetylene hydrogenation. Elucidation
of confinement of Ru NP and architecture of the network (2D
vs. 3D) on catalyst activity/selectivity is also one of the objec-
tives of the present study.
Although the covalent assembly of well-defined metal NP
could permit to direct substrates, or to create confined spaces
in order to produce better catalysts by means of CE, most of
the studies dealing with this type of material concentrated on
2. Results and Discussion
applications for biomedicine electronics or optics,[19] and they In previous works by some of us, 3D Ru NP covalent assemblies
are up to now only a limited number of studies dedicated to with homogeneous interparticle distances have been produced
Scheme 2. Carboxylic acid linkers for Ru NP: TPhC, TPhTC and HF.
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using spacer molecules such as a multi-adduct fullerene the presence of TPhC or TPhTC by using the reaction condi-
[15b]
(C66(COOH)12
)
or di-topic polymantane derivatives.[15a] The tions detailed in the experimental section. TEM images of the
distance between the NP is controlled in accordance to the as-synthesized Ru NP are presented in Figure 1. The use of the
different size of the ligands. Herein, the hexa-adduct functional- monodentate ligand TPhC leads to the formation of isolated
ized C60 (HF) ligand (Scheme 2) has been synthesized and em- NP with mean size of 1.7 0.7 nm (Figure 1a and Figure S3a).
ployed as tethering ligand for Ru NP in order to investigate the Differently, the use of the multi-topic compound TPhTC, what-
effect of the size of the ligand in opposition to the previously ever the Ru/TPhTC ratio used, leads to the production of assem-
[15b]
investigated multi-topic C66(COOH)12
.
Indeed, the interme- blies of Ru NP presenting mean diameter below 2 nm (Fig-
diary long chains present in HF should contribute to increase ure 1b–e). The size of these NP slightly increased with the Ru
the interparticle distance. Further, we hypothesized that the use content. These data are summarized in Table 1 and size histo-
of planar ligands could produce 2D assemblies. Hereof, carb- grams are given in Figure S3 of the SI.
oxylic acid triphenylene derivatives depicted in Scheme 2 have
been used as NP stabilizers. Both compounds, 2(6-(4-(carb-
oxy)phenoxy)hexyloxy)-3,6,7,10,11-pentakis(hexyloxy)triphenyl-
ene (TPhC) and 2,6,10-tris(6-(4-(carboxy)phenoxy)hexyloxy)-
3,7,11-trihexyloxytriphenylene (TPhTC) display the planar tri-
phenylene backbone, and one or three alkyl chains containing
each one the carboxylic acid moiety. The molecules possessing
substituted triphenylene backbone constitute a classical series
of discotic liquid crystal molecules.[23] However, the mono carb-
oxylic acid TPhC melts directly to an isotropic liquid and it is
not mesomorphic (Figure S1 of SI). In contrast, the tricarboxylic
acid derivative TPhTC shows an enantiotropic nematic meso-
phase (N) (from 55 to 113 °C) followed, on cooling, by a glass
transition, which is maintained in the second heating (Figure
S1 of SI). The nematic mesophase (N) was identified in optical
microscopy by its typical Schlieren texture (Figure S2 of SI). We
did not use TPhTC in the mesomorphic state, but the different
thermal behavior of TPhC and TPhTC reveals their different self-
assembly capacity. The extended aromatic sp2 basal plane and
the six substituents with three carboxylic ending groups at the
periphery position of the polyaromatic core could lead to ex-
tended and stable self-assemblies.[24] It has already been re-
ported that thanks to the aromatic sp2 basal plane, similar tri-
phenylene hexa-substituted derivatives afforded 2D metal-
organic frameworks, which provided significant activity for O2
electroreduction.[25] Triphenylene liquid crystals have been also
studied as materials for surface modification,[26] as stabilizers of
nanoparticles[27] and even as template of inorganic mesostruc-
tures.[28] To the best of our knowledge, this is the first time that
the ligands depicted in Scheme 2 are used for surface stabiliza-
tion in NP synthesis.
Figure 1. a) Ru@TPhC with a Ru/L ratio of 10:1; and Ru@TPhTC with Ru/L
ratio of b) 4:1; c) 20:1; d) 40:1; e) 70:1 and f) Ru@AdDC with Ru/L ratio of
10:1.[15a] (Scale bar = 50 nm).
HRTEM and HAADF-STEM analyses were also performed on
several samples (Figure 2) with different Ru/L ratio. Structural
analysis performed on the HRTEM images of the rare NP found
not aggregated, indicated that interplanar distances and angu-
lar relationships measured by 2D Fast Fourier Transform (2D-
FFT) analysis are consistent with single Ru crystalline domains
mostly showing the Ru hexagonal structure and quite seldom
the Mn-ꢀ cubic one.[29] The evidence of this is provided by the
HRTEM images displayed in Figure 2a, and it becomes apparent
when observing the 2D-FFT patterns calculated on the Regions
Of Interest (ROI) corresponding to distinct crystalline domains.
One single crystal domain per particle can be clearly observed.
In the case of Ru NP, at times the close proximity of single
crystalline seeds could appear as a sort of an elongated particle
composed by different crystalline domains (see the right-hand
side of Figure 2a). However, both the presence of small disconti-
nuities in these groups of close NP, and the different arrange-
ments observed for the atomic columns in different parts of
2.1 Synthesis and Characterization of 2D Ru NP
Assemblies
Ru NP were synthesized in THF by decomposition of [Ru- them, together with the different lattice spacing and zone axes
(η4-C8H12)(η6-C8H10)] under 3 bar of H2 at room temperature in detected, concur to indicate that the structures apparently ap-
Table 1. Mean size distributions, interparticle distances, ruthenium content, CO infrared frequency band of the Ru NP and Ru NP networks.
Catalyst
Ratio
Ru content [%][a]
NP size [nm][b]
NP size [nm][c]
Interparticle distance [nm][d]
νCO [cm–1 [e]
]
Ru@TPhC
Ru@TPhTC
Ru@TPhTC
Ru@TPhTC
Ru@TPhTC
Ru@HF
10:1
4:1
20:1
40:1
70:1
120:1
–
1.7 0.7
1.3 0.3
1.3 0.5
1.7 0.8
1.9 0.7
2.2 1.8
–
–
–
2.4
2.9
3.1
3.0
1928
1935
1939
1935
1926
1922
14.4
50.6
66.0
66.1
65.9
1.3–1.4
1.8
2.1
2.2
2.3
[a] By ICP. [b] By TEM. [c] By WAXS. [d] From SAXS. [e] By ATR-IR.
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pearing as an elongated seed are just constituted by different excluding Ru single atoms (Figure 2d and e), in agreement with
NP in close vicinity. Some further consideration is deserved by the WAXS analyses (Figure S4 of the SI). The WAXS analyses
the detection of a sole particle displaying Mn-ꢀ cubic structure revealed well-crystallized Ru NP in the hcp structure for samples
(Figure 2a). It is known that the HRTEM could provide with local
structural analysis of the particles it images, but, in case of con-
comitant presence of different crystal phases, such technique is
not capable to quantitatively determine which among the
phase is majority. This is due not only to the fact that HRTEM
generally investigates the crystal structure of a very limited
number of particles, but also that some phases may be less
detectable than others. Indeed, this is the case of Ru NP with
Mn-ꢀ cubic structure, of which the contrast is lower than the
one of the NP showing their expected hexagonal structure.
Such an effect combines with the NP very low size (about
1.5 nm), which further contributes to make their structure less
clear. Thus, the HRTEM imaging is just indicating that the Ru
NP contained in the sample with Ru/L ratio of 6:1 show both
the hexagonal and the Mn-ꢀ cubic crystal structure.
with a Ru/ligand ratio > 4. With the exception of Ru@TPhTC
with a Ru/L ratio of 4:1, which shows a very distorted structure,
all samples are consistent with metallic Ru NP in the hcp struc-
ture (Figure S4, top). This is confirmed in the RDF (Figure S4,
bottom) where similar patterns are observed. From the coher-
ence length, the size of the crystallites can be estimated to
2.2 nm for Ru@TPhTC - 70:1, 2.1 nm for Ru@TPhTC - 40:1,
1.9 nm for Ru@TPhTC - 20:1 and only 1.3 nm for Ru@TPhTC -
4:1. The Ru@TPhTC - 4:1 sample lacks characteristics from the
hcp structure and can be described as crystallized in the meta-
stable ꢀ-Mn structure,[29] as often observed for these very small
sizes.[30] This is likely the effect of the high ligand/metal ratio
that contributes to quench Ru NP growth right after the nuclea-
tion step.
Additionally, it is worth noting that the low contrast ob-
served on the TEM micrographs would suggest that the assem-
blies obtained are relatively thin in comparison to the ones
obtained with non-planar ligands such as polymantanes (both
adamantane and diamantane) dicarboxylic (Figure S3g and
h).[15a] This result suggests that the synthesis of 2D covalent
assembly of Ru NP is possible via the use of ligands containing
the planar triphenylene backbone. In order to corroborate the
two-dimensional nature of these assemblies, further characteri-
zations have been performed on these materials, including
electron tomography and atomic force microscopy (AFM). AFM
is commonly used to determine the thickness of 2D materi-
als.[31] As shown in Figure 3a, the material Ru@TPhTC synthe-
sized using a Ru/L ratio of 40:1 spreads evenly on the surface
of the wafer. Due to the difference in height and substrate of
the area covered by the material, the morphology and height
information of the sample can be clearly observed. The objects
have a measured thickness ranging from 3 to 12 nm (Figure 3b,
c and Figure S5 of the SI). Considering that the size of the Ru
NP is around 2 nm and taking into account the size of the
ligand estimated from small angle X-ray scattering (SAXS) analy-
ses (approximately 1 nm, see below), the thickness of the as-
sembly corresponds to one to four layers of metal NP. Besides,
the lateral size of the objects ranges from 0.1 to 1 μm, present-
ing a high aspect ratio, thereby confirming their 2D layered
structure.
The 3D reconstruction obtained via electron tomography
(see Figure 3e) confirms that the sample Ru@TPhTC – 40:1 is
constituted by small NP with spherical shape. Besides, the 3D
reconstruction of a large NP assembly (see Figure S6) allowed
to study the interparticle distance for different positions and
heights in the same quite large assembly of them. With this aim,
the NP mutual distances in the assembly have been sampled
in three diverse positions on the x-y plane, and at three diverse
height from the bottom, which is basically represented by the
TEM carbon grid where the particles were deposited. The three
histograms reported in Figure S6 clearly show that the interpar-
ticle distance in different parts (i.e., volumes corresponding to
Figure 2. a) and b) HRTEM images of Ru@TPhTC with a Ru/L ratio of
6:1 - structural analysis was performed on the single crystalline seeds: the
lattice spacings and zone axes are indicated in the HRTEM panels along with
the ROIs used to calculate the 2D-FFT patterns (reported in both right and
left panels). The Ru NP showing both the expected hexagonal and cubic Mn-
ꢀ structure are enclosed by square- and round-shaped frames, respectively.
b)-e) HAADF-STEM images of: b) and c) Ru@TPhTC with a Ru/L ratio of 20:1;
and d) and e) Ru@TPhTC with a Ru/L ratio of 40:1.
At a Ru/L ratio of 20:1, small quantities of clusters and even
Ru isolated atoms are shown around the NP in assemblies (Fig-
ure 2b and c). The Ru NP assemblies produced with a Ru/L the three colored boxes) of the large NP assembly is about the
ratio of 40:1 only display NP with Ru hcp crystalline structure same, and equal to a mean value of 2.4 1.2 nm.
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Figure 3. a) and b) AFM height images of Ru@TPhTC using 40:1 Ru/L ratio with c) height profile along the white dotted line; d) 3D rendering of the assembly;
and e) 3D reconstruction of Ru@TPhTC – 40:1 via electron tomography, where just some particles are imaged to provide a direct evidence of their spherical
shape.
SAXS analyses were also performed to reveal the arrange-
ment of Ru NP inside the assembly and the appearance of the
assembly of NP. A Kratky plot (q2I(q) vs. q) was employed to
highlight the different broad peaks of the X-ray scattering
curves (Figure 4). The SAXS data can be described as the scat-
tering from a multiscale organization of Ru NP assembly with a
sum of three contributions:
I(q)global = I(q)surface + I(q)corr + I(q)sphere * S(q)
To describe the region at low angles, we use a first term
I(q)surface that follows a power law function. The value of the
exponent reflects the roughness of the surface of the NP
assembly. All SAXS curves present at intermediate angles (0.01–
0.03Å–1) a broad peak reflecting the presence of a correlation
distance and can be described by the second term I(q)corr based
on adjustable Lorentzian function. The high angles contain
structural information on elementary Ru NP such as NP mean
diameter and mean interparticle distance, and can be modelled
Figure 4. SAXS patterns of Ru NP assemblies produced with the TPhTC ligand
with an equation of sphere I(q)sphere multiplied by a structural
(red curve, Ru@TPhTC - 20:1, yellow curve, Ru@TPhTC - 40:1, and green
factor S(q). All data were fitted with the model described above
curve, Ru@TPhTC - 70:1). The experimental SAXS curves are plotted in
log I(q)q2 fct log q representation in black line and the fitting curves corre-
sponding to the calculated SAXS curves from the model are plotted in
dashed line.
and the adjustable parameters are summarized in Table S1. The
first parameter corresponding to exponent of power law func-
tion (P) is close to 4 for Ru@TPhTC 20:1 (4) and Ru@TPhTC
70:1 (3.8) samples, corresponding to a well-define and smooth
interface. For Ru@TPhTC 40:1, this value decreases at 3.2 corre- layers. The measured values are consistent with those obtained
sponding to a rougher surface such as for the surface of fractal by AFM. The radius of the elementary Ru NP (R) increases
objects.[32] The correlation length observed at intermediates slightly with the proportion of ligand, giving a sphere radius
angles (ꢁ = 5–11 nm) could correspond to the thickness of the comprised between 0.75 and 1.2 nm consistent with EM obser-
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vations (0.65–0.95 nm). The peaks at high angle (> 0.1Å–1) rep- corresponds to a Ru/functional group ratio of 10:1. The HF li-
resent the average distance between NP detected at 0.18, gand was prepared for the first time in this work, and its synthe-
0.20 and 0.22 Å–1 for Ru@TPhTC samples 70:1, 40:1 and 20:1. sis consists in a two-step procedure. First, a malonate derivative
The correlation distances were calculated displaying the aver- containing two alkyne groups reacts through a Bingel-Hirsch
age of interparticle distances (Reff) at 3.1, 2.9 and 2.4 nm, for reaction with the fullerene C60, followed by an alkyne-azide 1,3-
samples 70:1, 40:1 and 20:1, respectively. As the length of the dipolar cycloaddition to give HF compound in low yield (see
ligand is the same for all Ru NP series this variation on the details in experimental section). The formation of a 3D assembly
distance is caused by the different Ru NP mean size diameter of Ru NP was first confirmed by TEM analyses (Figure 5a); the
(1.9 0.7, 1.7 0.8, and 1.3 0.5 nm, for Ru@TPhTC - 70:1, 40:1 size of the NP is 2.2 1.8 nm. WAXS analyses confirmed that
and 20:1, respectively), which fits well with a distance of about the Ru NP are well-crystallised in the hcp structure with a mean
1 nm for all cases due to the presence of the ligand (Table 1). particle size of 2.3 nm (Figure S8). SAXS analyses of the Ru@HF
The mean interparticle distance determined by ET for sample (Figure 5b) revealed an interparticle distance of 3.0 nm.
Ru@TPhTC samples 40:1 (2.4 1.2 nm) is in reasonable agree-
ment with the SAXS analysis (2.9 nm).
In that case, the peak is very broad, which was attributted
to the broad Ru particle size distribution (Figure S3f). Compar-
Finally, the thermal stability of the Ru@TPhTC - 40:1 was ing to the Ru NP assemblies described in a previous work by
evaluated by TPD/MS (Figure S7). Decarboxylation occurs at using the hexa-substituted fullerene C60, Ru@C66(COOH)12
190 °C, as ascertained by the detection of CO2. As the tempera- linker,[15b] the interparticle size is larger with HF, since the inter-
ture increases, decarbonylation (CO desorption) and decarbox- particle distance for Ru@C66(COOH)12 was 2.8 nm, with a Ru
ylation (CO2 desorption) is detected at around 300–400 °C. As NP size of 1.5 0.8 nm. Thus and as expected, the presence of
comparison, the TPhTC ligand decomposed in the temperature the intermediary long chains present in HF allows increasing
range of 420–440 °C, which indicates the decomposition is facil- the interparticle distance.
itated by Ru NP.
2.3 Surface Coordination Chemistry
2.2 Synthesis and Characterization of 3D Ru NP
The coordination of the stabilizing ligand onto the Ru NP sur-
face has been investigated by means of spectroscopic tech-
niques, including IR, solid state NMR using magic angle spin-
ning (MAS NMR), and X-ray photoelectron spectroscopy (XPS).
It has been previously demonstrated by some of us[15a,15b,33]
and others,[34] that carboxylic acid groups coordinate to the Ru
NP surface after losing their proton, giving rise to carboxylate
species together with surface hydrides. The carboxylate surface
species can be easily detected using IR spectroscopy; thus, the
IR spectra of the Ru@TPhTC samples produced at different
Ru/ligand ratio have been recorded and analyzed (Figure 6a).
The characteristic peak due to the C=O stretching of the carb-
oxylic acid groups of the ligand at 1680 cm–1 (Figure 6a, bot-
tom), vanishes in Ru@TPhTC samples, generating a new set
of peaks appearing at around 1578 and 1376 cm–1, assigned,
respectively, to the antisymmetric (νas(COO–)) and symmetric
(νs(COO–)) stretching vibrations of the carboxylate group. The
difference between νas(COO–) and νs(COO–) (Δν) in the IR spec-
tra is generally used to determine the coordination mode of
the carboxylate group.[35] For Ru@TPhTC samples, a Δν of
about 202 cm–1 was measured, which is attributed to a bridging
bidentate mode; in line with our previous results.[15a] Other
characteristic peaks of the ligand, such as the intense peaks at
1251 and 1164 cm–1 corresponding to the ether bonds, or the
peaks assigned to the triphenylene aromatic backbone, which
appear in the range of 1500–1600 cm–1, are observed in all
spectra, pointing out that the ligand is stable under the syn-
thetic conditions. An intense band at 1932 cm–1 was also ob-
served in all Ru samples, which indicates adsorbed CO on the
Ru NP surface; probably resulting from the decarbonylation of
the carboxylic acid and decomposition of the solvent of the
reaction, THF, as experimentally and theoretically demonstrated
elsewhere.[15a] In the case of the sample Ru@TPhTC with Ru/L
Assemblies
Likewise, Ru NP assembled with the HF ligand were synthesized
straightforwardly from [Ru(η4-C8H12)(η6-C8H10)] under 3 bar of
H2 at room temperature using a Ru/ligand ratio of 120:1, which
Figure 5. a) TEM image and b) SAXS pattern of Ru@HF produced using a
Ru/ligand ratio of 120:1.
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ratio of 70:1, the intensity of this band is weak, presumably that the Ru is coordinated to the ligand through oxygen atoms
because of a prolonged outgassing of this sample before analy- as observed before for Ru-carboxylate nanostructures.[15b]
sis, which favors CO desorption.[15a]
Concerning Ru@HF, infrared analysis show that, upon coordi-
nation of the HF ligand on the Ru NP surface, two new bands
appear at 1580 and 1395 cm–1, (Figure S11a) together with the
disappearance of the signals at 1720 cm–1 (C=O stretching),
when compared to the free HF ligand, corresponding to carb-
oxylate species coordinating to the Ru surface through a bridg-
ing bidentate mode (Δν = 185 cm–1). Adsorbed CO species
were also detected with a band at 1922 cm–1. The other bands
due to the ligand remained unchanged, which was attributed
to the stability of the ligand under synthetic conditions. The
triazole unit is identified by a band at 1551 cm–1 due to the
N=N bond,[38] and 1440 cm–1 due to N-C stretching.[39] The
band at 1731 cm–1 is due to the six carboxylate groups of the
malonate cycloadduct. The 13C SS-NMR spectrum (Figure S11b)
shows the presence of the ligand in the heterostructure. Char-
acteristic peaks of the 1,2,3- triazole unit (120.1 and 63.4 ppm),
the fullerene cage (141.4 and 66.2 ppm), quaternary carbon of
the cyclopropane (50.0 ppm) and the carbon atoms of the alkyl
chains (25.2 ppm) were detected in the spectrum.
These characterizations point for a similar stabilization of the
Ru NP in the 2D and 3D assemblies, which involves the coordi-
nation of the TPhTC and HF ligands through the carboxylate
bridging bidentate mode.
2.4 Hydrogenation of Phenylacetylene
Semi hydrogenation of phenylacetylene is an useful process to
purify styrene produced for polymerization.[40] From an environ-
mental point of view and cost, it has been shown that ruth-
enium is a greener heterogeneous catalyst compared to other
noble metals.[41] Surprisingly, even if colloidal Ru NP are usually
highly efficient (selective) hydrogenation catalysts,[42] reports
Figure 6. a) ATR-IR spectra of TPhTC and Ru@TPhTC with Ru/L ratio from 4:1
on the application of Ru NP for this specific catalytic reduction
to 70:1 (from bottom to top); and b) 1H-13C CP MAS SS-NMR spectrum of
are relatively scarce.[16a,43] We recently evidenced that for 3D Ru
Ru@TPhTC with a Ru/L ratio of 40:1.
NP assemblies produced from polymantane ligands, the Ru NP
MAS NMR with and without 1H-13C cross polarization (CP)
interparticle distance (steric effect) and electronic effects con-
trol the catalyst activity and selectivity.[15a] Increase of activity
was evidenced for electron rich Ru NP and/or for short interpar-
ticle distances. Oppositely, an increase of selectivity towards
styrene was observed on electro-deficient Ru NP and/or for
long interparticle distances.
1
were recorded for Ru@TPhTC - 40:1 sample, and the H-13C CP
MAS SS-NMR spectrum is depicted in Figure 6b (13C NMR of the
free ligand is shown on Figure S9). Peaks at 12.8, 25.4, 28.4 ppm
are attributed to the carbons of the alkyl chain, which link the
triphenylene core to the carboxylic acid moieties. The broad
peak centered at 67.1 ppm corresponds to the saturated
In this context, the 2D and 3D assemblies here prepared
carbons of the ether bonds besides the aromatic ring. The aro- were used as catalysts in the semi-hydrogenation of phenyl-
matic carbons appear in the range of 103.4 to 148.1 ppm. Al- acetylene to styrene under mild conditions, i.e. room tempera-
though hydrogenation of triphenylene with Ru NP have been ture and a constant H2 pressure of 5 bar. The results are listed
reported at 30–80 °C and 20 bar H2,[36] we did not find traces of in Table 2. Time-conversion/selectivity curves are presented on
hydrogenation of the triphenylene core under our conditions. Figure 7.
XPS of Ru@TPhTC - 40:1 (Figure S10, Table S2) reveals the
We analyzed the results obtained here in terms of steric and
presence of metallic Ru through the presence of two doublet electronic effects, which are correlated to interparticle distance
peaks of Ru 3d at 279.9 and 284.1 eV, and Ru 3p at 461.5 and and νCO of the CO adsorbed onto the Ru NP surface, respec-
483.7 eV.[37] The C 1s peak was deconvoluted into three contri- tively. The νCO frequency, which is a probe for the electronic
butions at 285.0 (C-C and C-H bonds), 286.4 (C-O bonds from effect of the ligands onto the Ru NP surface,[42] is different for
ether bonds), and 288.1 eV (O=C-O bonds). Two peaks at 530.8 the two samples, being (in cm–1): 1922 (Ru@HF) and 1935
and 532.3 eV of O 1s are in agreement with a carbonyl group (Ru@TPhTC); indicating a higher electronic density on the Ru
and a weak peak at 529.5 eV with a Ru–O bond, suggesting NP in the Ru@HF sample. When the electron density at the NP
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Table 2. Hydrogenation of phenylacetylene using Ru catalyst.[a]
Entry
Catalyst
Time [h]
Conv. [%]
S20 % [%]
S60 % [%]
TOF [h–1 [b]
]
TOFs [h–1 [c]
]
1
2
3
Ru@TPhTC - 40:1
Ru@HF - 120:1
5
3
8
64.0
86.1
10.6
57.5
53.5
51.2
–
46.5
134.3
3.8
15.6
70.2
5.8[e]
59.5
1.6 %Ru/O-CNT[15a]
67.8[d]
[a] Reaction conditions: 0.02 mmol of Ru, 412 mg (4.00 mmol) of phenylacetylene, 71 mg (0.50 mmol) of decane (internal standard), room temperature, 5 bar
H2, 25 mL of MeOH. [b] TOF in molPAconverted molRu–1 h–1 calculated according to surface Ru content at the time given in column reporting the reaction time.
[c] TOF calculated according to surface Ru content at 1 h. [d] Selectivity calculated at 10 % conversion. [e] TOF calculated according to surface Ru content at
8 h and Ru dispersion calculated as described in ref.[44]
.
Figure 7. Evolution of conversion (blue lines) and selectivity toward styrene (red lines) over time for the investigated catalysts: a) Ru@TPhTC - 40:1 and
b) Ru@HF - 120:1; product distribution over time for: c) Ru@TPhTC - 40:1; and d) Ru@HF - 120:1. (Black circle phenylacetylene, red diamond styrene, green
triangle ethylbenzene, and blue square ethylcyclohexane).
surface increases, favoring thus the π back-donation from the ylene under relatively mild reaction conditions using sup-
d Ru orbitals to the antibonding π* orbital of the alkyne/alkene, ported[43a] or colloidal[43c] Ru NP as catalysts has already been
we can expect a facilitated hydrogenation. Conversely, if the reported and is not surprising, even at room temperature.
charge transfer from the metal to the ligand results in elec- Ru@HF - 120:1 displayed the highest activity, which correlated
trodeficient Ru NP providing less π back-donation to the alkene, well with the fact that the Ru NP in Ru@HF display the highest
a weakened Ru–alkene bonding is obtained, which favors its electron density. The fact that both catalysts present a similar
quick desorption, and avoids overhydrogenation to produce selectivity cannot be correlated to this electronic effect.
ethylbenzene. From the results obtained we could thus ex-
pected that the Ru@HF catalyst will be more active, but less
selective than Ru@TPhTC.
As far as steric effects are concerned, it is thus worth noting
that from SAXS data these two catalysts present a similar inter-
particle distance. However, we can postulate that considering
the molecular structure of the HF ligand (Scheme 2) a more
sterically crowded environment should exist around the Ru NP
in the 3D Ru@HF architecture than in the 2D Ru@TPhTC one.
If this is the case, the higher TOF obtained with Ru@HF would
be in phase with a CE, as previously reported.[15a] However,
there also the selectivity towards styrene should be lower for
the Ru@HF catalyst in comparison with Ru@TPhTC.
Both catalysts were active for this hydrogenation reaction
displaying turnover frequencies (TOF) of 46.5 h–1 for Ru@TPhTC
and 134.3 h–1 for Ru@HF. The selectivity towards styrene is simi-
lar for both catalysts and relatively high (50–60 %) and constant
over time, up to 90 % conversion. In this conversion range, the
main products of reaction are styrene and ethyl benzene for
both catalysts. Above 90 % conversion the selectivity abruptly
decreases due to the formation of ethylbenzene and then ethyl-
A general tendency generally observed for ligand protected
cyclohexane (Figure 7). The total hydrogenation of phenylacet- NP catalysis is that the cleaner the metal surface, the higher
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the activity and the lower the selectivity.[45] In this sense, if we ligand it was determined to be only 0.25 %. We therefore attrib-
consider the Ru/L molar ratio calculated from elemental and ute this surprising result to the precision of the TEM measures
ICP analyses, it is around 73 and 22.5 for the Ru@HF and since after catalysis the NP are more aggregated, which is not
the case before catalysis. It is also worth mentioning that we
cannot discard a possible redispersion of the metallic phase
after catalysis with the formation of Ru single atoms. Although
we have not performed STEM-HAADF analyses to confirm that
possibility, this phenomenon has already been reported for
Ru/C catalysts.[47]
Ru@TPhTC catalysts, respectively. If we take into account the
Ru NP size, this roughly corresponds to -COOH/Rusurf ratio of
0.35 and 0.23 for the Ru@HF and Ru@TPhTC catalysts, respec-
tively (see experimental section for calculations). The lower ratio
obtained with the TPhTC ligand (cleaner metal surface) should
contribute to an increased activity and a decreased the selecti-
vity, which is not the observed tendency. Thus, as none of the
These results highlight the good stability of the covalent
classical ligand effects observed in selective hydrogenation can assemblies prepared as already reported in our previous stud-
satisfactorily explain the performances obtained in terms of ies.[15a]
both activity and selectivity, we tentatively attributed the spe-
cific behavior of the Ru@TPhTC catalyst (lower activity and sim-
3. Conclusion
ilar selectivity than Ru@HF) to the different spatial ordering of
the sample, 2D, in contrast to the 3D networks displayed for
Ru@HF. In the 2D assembly, the ratio between confined/uncon-
fined Ru NP should be much smaller than for the 3D assemblies.
These less marked effects of confinement, combined with the
electronic effects brought about by the ligands must be at the
origin of the lower performances obtained with the Ru@TPhTC
catalyst.
We have demonstrated here that the careful choice of the li-
gand allows producing in a controlled manner assemblies of Ru
metallic NP, which can be ordered in 2D or 3D networks. The
networks of small Ru NP are synthesized straightforwardly un-
der mild synthetic conditions. We have shown that electronic
and steric effects can be finely tuned, and therefore the cata-
lytic properties of the materials. It has already been shown that
long interparticle distances can be detrimental for activity in
the selective hydrogenation of phenylacetylene (weak CE),
while electron-deficient Ru surfaces can provide higher selecti-
vity towards the semi-hydrogenated product.[15a] The present
work proves that this is not always the case and that the dimen-
sionality of the NP networks should also be considered. Even if
instinctively 2D networks of metal NP should provide more ac-
tive catalysts, as a priori metal surface should be more readily
available, here it is not the case, argument which gives strength
to the importance of confinement effects, which seem to be
more easily reached when using 3D networks of metal NP.
To better delineate the performances of the Ru NP networks
prepared from the functionalized ligands we compared their
reactivity with the ones of individual unprotected Ru NP depos-
ited on carbon nanotubes functionalized with nitric acid (O-
CNT)[15a] that contains significant amounts of carboxylic groups
to stabilize Ru NP.[33] This catalyst present Ru NP size of 1.5 nm
(Figure S12) and show much lower conversions (Table 2, entry
3 and Figure S13) than the Ru NP networks. For this catalyst, in
which the Ru NP are not confined, the selectivity towards styr-
ene is higher than for the 2D and 3D NP networks. At low
conversions (< 10 %) the two products of the reaction are styr-
ene and ethyl benzene. High selectivity towards styrene and
relatively low activity are often obtained on supported or colloi-
dal Ru NP (see Table S3 for representative examples from the
literature). It thus appears that the confined Ru NP networks
prepared in this work present a lower selectivity than many
catalytic systems based on supported or colloidal Ru NP. CE
have been regularly reported to have a beneficial impact on
catalyst selectivity towards styrene in phenylacetylene
hydrogenation, the CE facilitating desorption of styrene from
metallic NP surface.[46] However, it is important to note that in
our confined catalysts the metal loading is extremely high (>
60 % w/w). Thus, the Ru NP density is extremely high and the
probability that a desorbed styrene molecule reached a new Ru
NP to be further hydrogenated is much higher than in the case
of conventional confined catalysts (see Scheme 1).
4. Experimental Section
4.1 General Methods: Solvents were purified by standard methods
or by an MBraun SPS-800 solvent purification system. 4-pentyn-1-
ol, triethylamine, 4-dimethylaminopyridine, malonyl chloride, CBr4,
C60 fullerene, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), sodium az-
ide (NaN3), 6-bromohexanoic acid, KI, CuBr·SMe2, sodium ascorbate,
QuadraSil® MP, phenylacetylene and decane were purchased from
Sigma-Aldrich and used as received. [Ru(COD)(COT)] [(1,5-cycloocta-
diene)(1,3,5-cyclooctatriene)ruthenium] was purchased from Na-
nomeps Toulouse, CO and H2 from Air Liquid. For column chroma-
tography silica gel 60 (230–400 mesh, 0.040–0.063 mm) was pur-
chased from E. Merck or by Sephadex LH20 (GE Healthcare, Barce-
lona, Spain) gel filtration.
Microwave irradiation experiments were performed using
a
The different catalysts prepared from TPhTC and HF linkers
were also analyzed by ICP and TEM after the catalytic reaction
(Figure S14 and Table S4). In all cases, the NP after catalysis are
slightly more aggregated, making the determination of their
size distribution more difficult. Surprisingly, the average NP
sizes is smaller than before the catalytic test. As this could be
the result from metal leaching, the ruthenium leaching was de-
termined by ICP analyses of the liquid phase after catalysis.
Monowave 300 (Anton Pear) apparatus. The temperature in the
sealed reaction vessel was monitored by an external surface sensor.
4.2 Characterization: The details of characterizations techniques
used in this work are provided in the Method section in the SI).
4.3 Ligand Synthesis
Synthesis of Carboxylic Functionalized Triphenylene (TPhC)
2-(4-(Methoxycarbonyl)phenoxy)hexyloxy)-3,6,7,10,11-pentakis-
Assemblies of TPhTC did not show any leaching, while for HF (hexyloxy)triphenylene (1): (Scheme 3) A mixture of 3,6,7,10,11-
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pentakis(hexyloxy)triphenylen-2-ol[48] (1.22 g, 1.64 mmol), methyl-4-
(6-bromohexyloxy)benzoate[48] (1.80 g, 5.73 mmol), and anhydrous
K2CO3 (0.80 g, 1.44 mmol) in 100 mL of dry butanone was refluxed
under nitrogen atmosphere for 24 h. After cooling to room tempera-
ture, the solvent was removed under vacuum, and then water
(200 mL) was added. The mixture was extracted with dichloro-
methane (5 × 30 mL). The organic fractions were combined and dried
with MgSO4. Filtration followed by solvent removal afforded the
crude product, which was purified by column chromatography (silica
gel, dichloromethane/hexane 1:3 v/v). The compound was isolated
as light yellow solid (1.33 g, 83 % yield). 1H NMR (CDCl3, 500 MHz)
O-CH3), 2.02–1.84 (m, 14H, CH2), 1.71–1.56 (m, 14H, CH2), 1.44–1.33
(m, 20H, CH2), 0.93 (m, 15H, CH3). IR (cm–1): ν (C=O): 1722.
2(6-(4-(Carboxy)phenoxy)hexyloxy)-3,6,7,10,11-pentakis(hexyl-
oxy)triphenylene (TPhC): To a suspension of compound (1)
(1.33 g, 1.36 mmol) in 140 mL of absolute ethanol, NaOH (1.69 g,
42.25 mmol) was added. After refluxing for 5 h, the solvent was
removed on a rotary evaporator. Water (120 mL) and dichloro-
methane (50 mL) were added to the solid residue obtained, and
the stirred mixture was treated with 36 % hydrochloric acid until
pH = 2. The organic phase was collected and the water solution
extracted again with dichloromethane (4 × 50 mL). The dichloro-
methane extracts were dried with anhydrous magnesium sulfate
δ(ppm) = 7.97 (d, 2H, ArH, AA′ part of AA′XX′ spin system, N = JAX
+
JAX′ = 8.98 Hz, JAA′ ~ JXX′), 7.83 (s, 6H, TripH), 6.90 (d, 2H, ArH, XX′ part
of AA′XX′ spin system, N = JAX + JAX′ = 8.98 Hz, JAA′ ~ JXX′), 4.23 (m, and filtered. The solvent was removed on a rotary evaporator to
12H, TriPh-O-CH2), 4.04 (t, 2H, ArH-O-CH2, J = 6.40 Hz), 3.88 (s, 3H, obtain the product as a light yellow solid, which was dried under
Scheme 3. Synthesis procedure of TPhC.
Scheme 4. Synthesis procedure of TPhTC.
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1
vacuum. (1.21 g, 93 % yield). H NMR (CDCl3, 500 MHz) δ (ppm) =
10.86 (s, 1H, OH), 8.04 (d, 2H, ArH, AA′ part of AA′XX′ spin system,
N = JAX + JAX′ = 9.01 Hz, JAA′ ~ JXX′), 7.84 (s, 6H, TriPh), 6.93 (d,
2H, ArH, XX′ part of AA′XX′ spin system, N = JAX + JAX′ = 9.01 Hz,
JAA′ ~ JXX′), 4.23 (m, 12H, TriPh-O-CH2), 4.06 (t, 2H, ArH-O-CH2, J =
6.48 Hz), 2.02–1.86 (m, 14H, CH2), 1.72–1.54 (m, 14H, CH2), 1.45–
1.34 (m, 20H, CH2), 0.93 (m, 15H, CH3). 13C {1H} NMR (CDCl3,
126 MHz, Me4Si) δ(ppm) = 171.43 (C=O), 163.60 (sp2-C, O-CPh),
149.03, 149.02, 148.99, 148.97, 148.96, 148.85 (sp2-C, O-CTriPh),
132.32 (sp2-C, HA-CPh), 123.71, 123.67, 123.65, 123.58 (sp2-C, CTriPh),
121.41 (sp2-C, HOOC-CPh), 114.16 (sp2-C, Hx-CPh), 107.47, 107.46,
107.39, 107.36, 107.25 (sp2-C, H-CTriPh), 69.79, 69.74, 69.71, 69.62,
69.52, 68.10 (O-CH2), 31.69, 31.67, 29.44, 29.43, 29.11, 25.98, 25.85,
22.66 (CH2), 14.05 (CH3). IR (cm–1): ν (C=O): 1690. Anal. calcd. (%) for
C61H88O9: C, 75.90; H, 9.19; O, 14.92; found C, 75.78; H, 9.02. DSC
(Transition temperature and enthalpy in parentheses; data referred
to the second heating scan) = Crystal → Isotropic liquid 63.6 °C
(33.2 kJ mol–1).
tures and enthalpies in parentheses; data referred to the second
heating scan) = Glass → Nematic 58.5 °C, Nematic → Isotropic liq-
uid 113.6 °C (3.3 kJ mol–1).
Synthesis of Hexa-Substituted Fullerene (HF)
Di(pent-4-yn-1-yl) Malonate (1): (Scheme 5) 4-pentyn-1-ol
(0.88 ml, 9.46 mmol), NEt3 (1.34 mL) and 4-dimethylaminopyridine
(DMAP) (11.56 mg, 0.0946 mmol) were successively dissolved in di-
chloromethane (25 ml) under inert atmosphere. The mixture was
cooled down to 0 °C, and a solution of malonyl chloride (0.47 mL,
4.73 mmol) in 1–2 mL of dichloromethane was added dropwise.
After 30 min, the reaction mixture was warmed up to room temper-
ature and stirred overnight. The reaction solution was treated with
20 mL of HCl (1
M) twice, and then by the same volume NaHCO3
saturated solution for two times. After, the organic phase was
washed once by 20 mL of brine, dried with MgSO4 and filtered.
After evaporation of the solvent the crude product was purified
by flash chromatography (dichloromethane/hexane, 3:1) to obtain
colorless oily product. (616.2 mg, 55 % yield). 1H NMR (CDCl3,
300 MHz) δ(ppm) = 4.30 (t, J = 6.3 Hz, 4H), 3.4 (s, 2H), 2.31 (td,
J = 7.0, 2.7 Hz, 4H), 1.99 (t, J = 2.7 Hz, 2H), 1.89 (m, 4H).
Synthesis of Tricarboxylic Functionalized Triphenylene (TPhTC)
2,6,10-Tris(6-(4-(methoxycarbonyl)phenoxy)hexyloxy)-3,7,11-tri-
hexyloxytriphenylene (2): (Scheme 4). A mixture of 2,6,10-tri-
hydroxy-3,7,11-trihexyloxytriphenylene[49] (1.83 g, 3.17 mmol),
methyl-4-(6-bromohexyloxy)benzoate[50] (9.00 g, 28.6 mmol), and
anhydrous K2CO3 (15.79 g, 114.2 mmol) in 100 mL of dry butanone
was refluxed under nitrogen atmosphere for 24 h. After cooling to
room temperature, the solvent was removed under vacuum, and
then water (100 mL) was added. The mixture was extracted with
dichloromethane (3 × 30 mL). The organic fractions were combined
and dried with MgSO4. Filtration followed by solvent removal af-
forded the crude product, which was purified by column chroma-
tography (silica gel, ethyl acetate/hexane 3:1 v/v). The compound
was isolated as a light yellow solid (2.25 g, 55.4 % yield). 1H NMR
(CDCl3, 500 MHz) δ (ppm) = 7.97 (d, 6H, ArH, AA′ part of
AA′XX′ spin system, N = JAX + JAX′ = 8.92 Hz, JAA′ ~ JXX′), 7.84 (s, 3H,
TriPh), 7.83 (s, 3H, TriPh), 6.90 (d, 6H, ArH, XX′ part of AA′XX′ spin
system, N = JAX + JAX′ = 8.92 Hz, JAA′ ~ JXX′), 4.23 (m, 12H, TriPh-O-
CH2), 4.04 (t, 6H, ArH-O-CH2, J = 6.40 Hz), 3.88 (s, 9H, O-CH3), 2.02–
1.84 (m, 18H, CH2), 1.72–1.53 (m, 18H, CH2), 1.38 (m, 12H, CH2), 0.92
(t, 9H, CH2, J = 6.92 Hz). IR (cm–1): ν (C=O): 1716.
Th-symmetrical C60 Hexa(di(pent-4-yn-1-yl)cyclopropane-1,1-di-
carboxylate) (2): (Scheme 5). CBr4 (8.8 g, 26 mmol), compound (1)
in Scheme S3 (616 mg, 2.6 mmol) and fullerene (187.4 mg,
0.26 mmol) were dissolved in dry toluene (500 mL). DBU (0.78 mL,
5.2 mmol) was introduced into the mixture dropwise. The color of
the solution changed from violet to red. The mixture was kept stir-
ring under inert atmosphere for 72 h at room temperature. After
that, the organic solution was extracted with 100 mL of saturated
Na2S2O3 solution, 150 mL of HCl (1 M), deionized water twice, and
finally with 100 mL of brine. The organic layer was dried with
MgSO4 filtered and concentrated under reduced pressure. The
crude product was purified by flash chromatography using di-
chloromethane as eluting solvent. The product was isolated as or-
ange solid (289.9 mg, 53 % yield). 13C NMR (CDCl3, 75 MHz, Me4Si)
δ (ppm) = 164.0 (C=O), 146.1 (sp2-C C60), 141.4 (sp2-C C60), 82.8 (C≡ ),
70.2 (CH≡ ), 69.4 (sp3-C C60), 65.7 (CH2), 45.7 (tert-C), 27.5 (CH2), 15.5
(CH2).
6-Azido-hexanoic Acid (3): (Scheme 5) Sodium azide (NaN3, 1 g,
26 mmol), 6-Bromohexanoic acid (1 g, 5 mmol) and KI (170 mg,
1.02 mmol) were dissolved into deionized H2O (15 mL) in a
30 mL glass vial. The reaction was carried out in a microwave at
120 °C for 30 min, and cooled down to 55 °C for removing. The
mixture was extracted with diethyl ether (20 mL) three times. The
organic layer was washed with brine once and dried with MgSO4. A
colorless liquid was afforded after concentration at reduced pressure
(436 mg, 69 % yield). IR (cm–1): 2090.19 (s, N3), 1703.23 (s, C=O),
1250.95 (m, C-O). 13C NMR (CDCl3, 175 MHz, Me4Si) δ (ppm) = 180.3
(C=O), 51.5 (N-CH2), 34.1 (CH2), 28.8 (CH2), 26.4 (CH2), 24.4 (CH2).
2,6,10-Tris(6-(4-(carboxy)phenoxy)hexyloxy)-3,7,11-trihexyl-
oxytriphenylene (TPhTC): To a solution of 2,6,10-tris(6-(4-(meth-
oxycarbonyl)phenoxy)hexyloxy)-3,7,11-trihexyloxytriphenylene[49]
(1.90 g, 1.48 mmol) in 100 mL of absolute ethanol, NaOH (3.56 g,
89.1 mmol) was added. After refluxing for 6 h, the solvent was re-
moved on a rotary evaporator. Glacial acetic acid (125 mL) was
added and the mixture refluxed for 2 h giving rise to a white solid.
The solid was collected by filtration, washed first with cold water
(3 × 50 mL), then with cold acetone (3 × 50 mL) and finally dried
under vacuum. (1.60 g, 87.1 % yield). 1H NMR ([D6]DMSO, 500 MHz)
δ(ppm)= 12.56 (s, 3H, OH), 7.94 (s, 3H, TriPh), 7.93 (s, 3H, TriPh), 7.85 Th-symmetrical C60 hexa(6,6′-((((cyclopropane-1,1-dicarbonyl)-
(d, 6H, ArH, AA′ part of AA′XX′ spin system, N = JAX + JAX′ = 8.92 Hz,
JAA′ ~ JXX′), 6.96 (d, 6H, ArH, XX′ part of AA′XX′ spin system, N = JAX
+ JAX′ = 8.92 Hz, JAA′ ~ JXX′), 4.19 (m, 12H, TriPh-O-CH2), 4.01 (t, 6H,
ArH-O-CH2, J = 6.42 Hz), 1.85–1.71 (m, 18H, CH2), 1.63–1.42 (m, 18H,
CH2), 1.35–1.22z (m, 12H, CH2), 0.82 (t, 9H, CH3, J = 6.87 Hz). 13C
bis(oxy))bis(propane-3,1-diyl))bis(1H-1,2,3-triazole-4,1-diyl))di-
hexanoic Acid): (Scheme 5, HF). Compound (Scheme 5 (2))
(120 mg, 0.056 mmol) and 6-azido-hexanoic acid (177.2 mg,
1.129 mmol) were dissolved in DMSO (3 mL). Copper bromide di-
methyl sulfide complex, CuBr·SMe2, (81.2 mg, 0.395 mmol) and so-
{1H} NMR ([D6]DMSO, 126 MHz, Me4Si) δ(ppm) = 167.44 (C=O), dium ascorbate (134.2 mg, 0.677 mmol) were added into the mix-
162.72 (sp2-C, O-CPh), 149.00, 148.98 (sp2-C, O-CTriPh), 131.75 (sp2-C, ture successively. The solution was stirred with a stirrer twined with
HA-CPh), 123.39, 123.35 (sp2-C, CTriPh), 123.26 (sp2-C, HOOC-CPh), copper wire under inert atmosphere at room temperature for 48 h.
114.56 (sp2-C, Hx-CPh), 107.55, 107.49 (sp2-C, H-CTriPh), 69.13, 69.08,
68.12 (O-CH2), 31.53, 29.35, 29.05, 25.97, 25.83, 25.76, 22.58 (CH2),
Then, QuadraSil® MP was added to the solution and stirred for
15 min to remove Cu. After filtration the solution was passed
through a Sephadex LH-20 column with dichloromethane/meth-
14.29 (CH3). IR (cm–1): ν (C=O): 1678. Anal. calcd. (%) for C75H96O15
:
C, 72.79; H, 7.82; found C, 72.81; H, 7.70. DSC (Transition tempera- anol (1:1) as elution. The solution was washed by centrifugation
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Scheme 5. Synthesis of the hexa-substituted fullerene C60 (HF) using a Bingel-Hirsch hexaadduct and click chemistry.[51]
with AcOEt (10 min, 6000 rpm) for three times. A dark red solid was
isolated (79 mg, 36 % yield). IR (cm–1): 3140 (w, C-H), 1720 (s, C=O), NMR (DMSO, 175 MHz, Me4Si): δ = 207.0 (COOH), 163.3 (C=O)145.5
1459 (w, triazole), 1210 (s, C-O), 1006 (m, C-O). 1H NMR (DMSO, (sp2-C, C60), 141.2 (sp2-C, C60), 123.0 (N-CH=C), 69.2 (sp3-C, C60), 67.0
700 MHz): δ = 12.00 (s, 1H, COOH), 7.89 (s, 1H, N-CH=C), 4.33 (s, 2H, (N-CH2), 49.6 (O-CH2), 46.0 ppm (tert-C), 29.9 (CH2), 28.2 (CH2), 26.0
N-CH2), 4.27 (s, 2H, O-CH2-), 2.63 (s, 2H, CH2), 2.23 (s, 2H, CH2), 1.95 (CH2), 24.6 (CH2), 21.8 (CH2).
(s, 2H, CH2), 1.77 (s, 2H, CH2), 1.49 (s, 2H, CH2), 1.21 (s, 2H, CH2). 13
C
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Table 3. Calculation of the -COOH/Rusurf ratio.
Rutotal/L
L/Rutotal
L/Rusurf
–COOH/Rusurf
Ru@HF
Ru@TPhTC
73
22.5
0.0137
0.0444
0.029 (2.2 nm - 47.7 % Rusurf)
0.076 (1.7 nm - 58.1 % Rusurf)
0.35 ( × 12 L/Rusurf)
0.23 ( × 3 L/Rusurf)
4.4 Synthesis of Ru NP
surface of the NP = Nshell/Ntotal*100 %. For calculation of the COOH/
Rusurf ratio see Table 3.
In
a
typical experiment, ruthenium precursor [Ru(η4-C8H12)-
(η6-C8H10)] and the corresponding ligand were dissolved in THF in
a Fisher-Porter bottle and the solution was stirred 1 h (30 min for
HF) at room temperature. After this period of time, 3 bar of dihydro-
gen were introduced into the bottle. The reaction was allowed to
react 16 h at room temperature under vigorous stirring. The excess
Acknowledgments
We acknowledge the Centre National de la Recherche Scientif-
ique (CNRS) and Institute Nationale Polytechnique (INP). This
of H2 was eliminated and the volume of the solvent was reduced work was supported by the Agence Nationale de la Recherche
under vacuum. The black solid from the suspension was precipi-
tated after the addition of 200 mL of pentane. After filtration under
argon with a cannula, the black solid powder was washed twice
with pentane (200 mL) and filtered again before drying under vac-
uum overnight. For typical ratio and ligand studied, the quantities
of the reactants are detailed hereafter:
(ANR project ANR-16-CE07-0007-01, Icare-1), which is gratefully
acknowledged.
Keywords: Metallic nanoparticles · Ruthenium · Covalent
assembly · Acetylene hydrogenation · Confinement effect
Ru@TPhC - 10:1: 50 mg (0.159 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
13.8 mg (0.0143 mmol) of TPhC, and 20 mL of THF. Yield: 21.7 mg.
Ru@TPhTC - 4:1: 200 mg (0.634 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
200 mg (0.162 mmol) of TPhTC, and 80 mL of THF. Yield: 156.1 mg.
Anal.: Ru, 14.4 %.
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Ru@TPhTC - 20:1: 200 mg (0.634 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
40.6 mg (0.033 mmol) of TPhTC, and 80 mL of THF. Yield: 65.7 mg.
Anal.: Ru, 50.6 %.
Ru@TPhTC - 40:1: 200 mg (0.634 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
20.3 mg (0.016 mmol) of TPhTC, and 80 mL of THF. Yield: 81.7 mg.
Anal.: Ru, 66.0 %; C, 17.0 %; H, 1.8 %.
Ru@TPhTC - 70:1: 200 mg (0.634 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
10.7 mg (0.009 mmol) of TPhTC, and 80 mL of THF. Yield: 63.5 mg.
Anal: Ru, 66.1 %.
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Ru@HF - 120:1: 130 mg (0.412 mmol) of [Ru(η4-C8H12)(η6-C8H10)],
13.3 mg (0.0034 mmol) of HF, and 2.6 mL of methanol and 26 mL
of THF. Yield: 50.4 mg. Anal.: Ru, 65.9 %; C, 16.0 %; H, 1.2 %; N, 2.6 %.
4.5 Catalytic Hydrogenation of Phenylacetylene
In a typical catalytic reaction, a mixture of phenylacetylene (4 mmol,
412 mg), decane (0.5 mmol, 71 mg) and Ru NP catalyst (0.02 mmol
of Ru) were dispersed in methanol (25 mL) in a magnetically stirred
autoclave with Teflon inner cylinder. The autoclave was purged
three times with H2. The autoclave was pressurized with 5 bar of
H2 at room temperature and stirred at 1500 rpm. Under such condi-
tions, external mass transfer limitation should not be relevant.[15a]
The suspension was continuously stirred until the end of the reac-
tion. Gas chromatography (GC) was used to identify the products.
After catalysis, samples were taken for TEM analyses, also, the % of
Ru on the filtered catalytic solution was ascertained by ICP.
Calculation of Ru Surface Content
The number of Ru atoms in hcp cell (N) is 6. Ru atom radius (RRu) is
0.214 nm. The volume of Ru cell is 0.0817 nm3. RNP represents the
radius of the NP. The volume of all Ru atoms on the shell of NP:
Vshell = Vtotal – Vcore = 4/3πRNP3 – 4/3π(RNP-RRu)3, Vtotal meaning the
volume of one Ru nanoparticle, Vcore presenting the volume of the
NP excluded the one outer layer of atoms. The numbers of Ru at-
oms on the shell Nshell = N*Vshell/0.0817. The number of total Ru
atoms Ntotal = N*Vtotal/0.0817. The percentage of Ru atoms on the
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Received: July 23, 2020
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