Advanced nanostructured catalysts for hydroboration

Article abstract of DOI:10.1016/j.cattod.2014.11.038

Metal nanocrystals have been prepared in onium salts using supercritical carbon dioxide assisted synthesis. During the process, metal salts precursors are reduced by H₂ in an organic solvent free media, the onium salts allowing both the stabili

Full text of DOI:10.1016/j.cattod.2014.11.038

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Catalysis Today
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Advanced nanostructured catalysts for hydroboration
Virginie Liautarda, Oana Pascub, Cyril Aymonierb,∗, Mathieu Pucheaulta,∗
a CNRS, Université de Bordeaux, ISM, UMR 5255, 351 cours de la libération, F-33405 Talence, France
b CNRS, Université de Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal nanocrystals have been prepared in onium salts using supercritical carbon dioxide assisted syn-
thesis. During the process, metal salts precursors are reduced by H2 in an organic solvent free media, the
onium salts allowing both the stabilization of the nanostructured material and the preparation of an air
and moisture stable powder made of embedded metal nanocrystals. Those catalysts proved to be highly
effective in the hydroboration of alkyne process.
Received 28 October 2014
Received in revised form
24 November 2014
Accepted 29 November 2014
Available online xxx
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Metal nanoparticle
Organic solvent free process
Onium salt
Hydroboration
1. Introduction
Although the reagents/product are similar, the reaction mechanism
is different and is supposed to involve a syn-addition of the boryl-
In many ways, hydroboration [1] remains one of the key
reactions used in modern synthetic chemistry to selectively func-
tionalize insaturations [2]. When performed on carbon–carbon
triple bonds, the resulting vinylboranes can be subsequently used
in various transformations, including transition metal catalyzed
cross-coupling. To promote this reaction, numerous homogeneous
catalytic systems have been developed, mostly based on late tran-
sition metal complexes [3]. Group-IV metal (Ti, Zr) [4] were proved
to be efficient as well. In order to apply this versatile chemistry
at a larger scale, heterogeneous catalysts are required. However,
due to reactivity and selectivity issues, only few heterogeneous
systems have so far been developed. For homogenous complexes
immobilization several approaches are described. Using fluorous
tagged ligand, rhodium complexes can be trapped in a perfluori-
nated solvent, efficiently promoting the hydroboration for several
cycles [5]. A very nice approach has been used by Fernandez et al.
[6] to intercalate cationic rhodium complexes in montmorillonite
interlayers. Even if they mostly studied alkene hydroboration, this
example is one of the most efficient systems to recycle hydrobora-
tion catalyst. Recently a copper-catalyzed vinylboronate formation
was disclosed using bis(pinacolato)diboron as a boron source [7].
sodium onto the triple bond [7]. This reaction is somehow related
to the gold nanoparticles (NPs) catalyzed diboration of alkynes
showing firstly that NPs could promote carbon-bond formation [8].
Finally, it has recently been found that iridium nanoparticles favor
hydroboration of alkene and alkyne [9].
Despite the large use of hydroboration to yield valuable build-
ing blocks, no general studies have been reported on transition
metal nanoparticles (NPs)/nanocrystals (NCs) catalyzed hydrobo-
ration. This could be a first step toward the design of an active bulk
heterogeneous catalyst.
With this work we would like to show/demonstrate how the
use of onium salts (OSs) combined with supercritical carbon diox-
ide (scCO2) technology has enabled the preparation of a vast variety
of metal nanocrystals stabilized by OSs as good nanocatalysts for
hydroboration (Scheme 1). For semi-heterogeneous catalysis, the
surface state is critical in order to obtain a good catalytic activity.
Hence, we developed a method for organic solvent free prepara-
tion of NCs embedded in OSs. Previously, we have shown that a
powder of onium salt containing palladium NPs could be obtained
by simply mixing trimethylbutylammonium hexafluorophosphate
([tmba]PF6) with a palladium salt above the onium salt melting
point (m.p. 176 ◦C) [10]. This concept is generalized herein by
using other metal precursors (Rh, Ir, Pt, Ru) and OSs with lower
or very high melting points. In all cases, the use of supercritical flu-
ids, supercritical carbon dioxide in our case, was crucial. Indeed,
among numerous properties displayed by supercritical fluids, we
∗
Corresponding authors.
E-mail addresses: m.pucheault@ism.u-bordeaux1.fr (C. Aymonier),
aymonier@icmcb-bordeaux.cnrs.fr (M. Pucheault).
http://dx.doi.org/10.1016/j.cattod.2014.11.038
0920-5861/© 2014 Elsevier B.V. All rights reserved.
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Scheme 1. Sketch of hybrid organic/inorganic NCs, M@OS labeled as M@TBAB, M@BnTAB, M@CTAB and M@CTANTf2 obtained by onium salts cation/anion modulation.
method: 70 ◦C for 1 min then 20 ◦C min−1 until 230 ◦C then 6 min at
230 ◦C.
have used the high solubility of scCO2 in liquid OSs which enables
the fast transport of metal salts inside the ionic phase.
2. Experimental
2.2. Synthesis procedure for nanocatalysts preparation
2.1. Materials and methods
Synthesis in supercritical fluid media required a high pres-
sure/high temperature home-made stirred batch reactor (made
of stainless steel), with a volume of 60 mL. Reaction parameters
(pressure and temperature) were monitored with a pressure sen-
sor inside the reactor and an external heating mantle coupled with
a thermocouple placed inside the reactor.
In the reactor were mixed the onium salt with the metal precur-
sor (1 wt% metal) both in powder form. Using gas bottle containing
a mixture of CO2 + H2 in volume ratio 80:20 we first loaded 3.4 bar
of this mixture. During heating (100 ≤ T ≤ 185 ◦C), CO2 was loaded
within the reactor through a high pressure pump to reach the
desired pressure of 230 bar. The set temperature and pressure were
maintained constant for 30 min, when the chemical reaction takes
place. At the end of reaction, the reactor was depressurized and CO2
vented through the reactor for few more minutes as cleaning and
drying steps. The final product, nanocrystals embedded in the solid
matrix of ammonium salt was recovered as dark powder and used
directly in the hydroboration reaction. A sketch of the experimental
setup is presented elsewhere [12].
The metal organic precursors were purchased from Aldrich
and Strem Chemicals and used as received: ruthenium (III)
acetylacetonate (Ru(acac)3, 97%), rhodium (II) trifluoroacetate
dimer [Rh(tfa)2]2, 95%), chloro-1,5-cyclooctadiene iridium (I)
dimer ([Ir(cod)Cl]2, 99%) and platinum (II) hexafluoroacety-
lacetonate (Pt(hfa)2, 98%). The onium salts were purchased
from Aldrich as following: (a) tetrabutylammonium bromide
(TBAB), (b) benzyltrimetylammonium bromide (BnTAB), (c)
cetyltrimethylammonium bromide (CTAB). The cetyltrimethy-
lammonium bis(trifluoromethyl-sulfonyl)imide (CTANTf2) was
prepared according to a previously reported methodology [11].
Phenylacetylene and pinacolborane were purchased from Alfa
Aesar and used as received.
Final materials morphologies, labeled M@TBAB, M@BnTAB,
M@CTAB and M@CTANTf2 respectively (where M = Ru, Rh, Ir and
Pt) were characterized by conventional (TEM-JEOL 2100) and
high resolution (TEM-FEG HR-JEOL 2200FS) transmission electron
microscopy. The samples were prepared by dissolving the powder
hybrid nanocatalyst in an organic solvent (ethanol or acetone) and
deposited by drop casting on a carbon grid.
As metal precursors, Ru(acac)3, [Rh(tfa)2]2, [Ir(cod)Cl]2 or
Pt(hfac)2, commonly employed for the nanostructured mate-
rial fabrication in supercritical fluids media, were used [13].
The materials prepared by the above described procedure and
the experimental parameters used are listed in the following
Table 1. Upon reduction, the counteranion is protonated leading to
Powder XRD analysis on the above mentioned systems were
performed using an X-ray diffractometer with Cu ꢀK␣ radiation
(PANalytical X’Pert Pro). FTIR reflection measurements were made
using a Bruker spectrophotometer working in the 7500–400 cm−1
range.
Table 1
All catalytic reactions were carried out under an argon atmo-
sphere. 1H NMR was recorded on Bruker Avance 300 FT 300 MHz
spectrometers using CDCl3 as internal reference. The chemical
shifts (ı) and coupling constants (J) are expressed in ppm and
Hz, respectively. The following abbreviations were used to explain
the multiplicities: s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet. GC–MS analysis were performed with a HP 6890
series GC-system equipped with a J&W Scientific DB-1701 capillary
column, a HP 5973 mass selective detector (EI) using the following
Precursors and reaction temperatures used for the preparation of M@OS nanocata-
lysts, where OS = TBAB, BnTAB, CTAB and CTANTf2and M = Pt, Ir, Rh and Ru.
Precursor type Tr (◦C) scCO2 – 230 bar/30 min
TBAB
BnTAB
CTAB
CTANTf2
Ru(acac)3
[Rh(tfa)2]2
Ir(cod)2Cl
Pt(hfac)2
185
150
100
100
Ru@TBAB Ru@BnTAB Ru@CTAB Ru@CTANTf2
Rh@TBAB Rh@BnTAB Rh@CTAB Rh@CTANTf2
Ir@TBAB
Pt@TBAB
Ir@BnTAB
Pt@BnTAB
Ir@CTAB
Pt@CTAB
Ir@CTANTf2
Pt@CTANTf2
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Fig. 1. TEM images of rhodium NCs stabilized by 4 OS, such as Rh@TBAB (a), Rh@BnNMe3Br (b), Rh@CTAB (c) and Rh@CTANTf2 (d) taken as our reference system. NCs sizes
were obtained from Gaussian size distribution by counting more than 150 NCs. HRTEM (e) and surface area electron diffractions (SAED) images corresponding to Rh@TBAB
(f).
1,3-diketones (for Ru(acac)3, [Rh(tfa)2]2, and Pt(hfac)2 precursors),
cyclooctane and HCl (for [Ir(cod)Cl]2; all of which are vented
during depressurization.
(d, 1H, J = 14.9 Hz), 1.29 (s, 12H); MS (EI) tR = 8.38 min; m/z: 105.1
(42%), 130.0 (100%), 144.1 (45%), 215.1 (30%), 230.1 (M+, 69%).
1-Phenylvinylboronic acid pinacol ester (˛-3): [16] 1H NMR
(300 MHz, CDCl3) ı 7.53–7.46 (m, 2H), 7.39–7.28 (m, 4H), 6.10–6.03
(m, 2H), 1.32 (s, 12H); MS (EI) tR = 8.48 min; m/z: 105.1 (33%), 114.1
(40%), 129.1 (100%), 144.1 (76%), 215.1 (23%), 230.1 (M+, 40%).
2.3. General procedure for phenylacetylene hydroboration
Pinacolborane (1.0 mmol) and then phenylacetylene (1.0 mmol)
were added under argon to the M@OS (0.1 mol%) contained in a
15 mL reaction tube. The mixture was stirred at 85 ◦C for 23 h.
The reaction mixture was then diluted in dichloromethane and
filtrated over a pad of silica. After washing twice with 10 mL
of dichloromethane the filtrate was concentrated under vacuum
to give the corresponding vinylborane as a mixture of isomers.
Product distribution was determined by GC/MS. Conversion is
determined using the relative areas in GC/MS and according to
mesitylene as internal standard. The spectral data were in agree-
ment with those reported in the literature.
3. Results and discussion
3.1. Synthesis and characterization of materials
In this work, the metallic nanocrystals were fast and easily pre-
pared by H2 reduction of metal precursor mediated by scCO2. This
technique allowed scCO2 and melted OS to play the solvent role
leading to dissolution, decomposition and metal formation. The use
of various OS as stabilizers (Scheme 1) is expected to influence NCs
morphology (size, shape), dispersion and surface properties. These
characteristics were analyzed using TEM measurements and the
surface properties influence was investigated using alkene hydrob-
oration. As the hydroboration is known to be efficiently catalyzed
by homogeneous rhodium catalysts as Wilkinson’s catalyst or het-
erogeneous Rh complexes immobilized in MMT [6], our first M@OS
system was designed with rhodium, the TEM micrographs proving
the synthesis of dispersed, very small (∼2 nm, Fig. 1a-d) and highly
crystalline Rh@OS NCs (the crystalline fringes being highlighted
with white circles, Fig. 1e).
It was studied the potential of the as prepared system of Rh@OS
NCs in the neat alkyne hydroboration. We examined the catalytic
properties using phenylacetylene as a terminal alkyne (Scheme 2),
which allows three possible regio- and stereoisomers. Pinacol
borane, as obtained boronic ester is relatively stable and is a useful
building-block. Using 0.1 mol% of catalyst at 85 ◦C it afforded con-
version exceeding 76% with selectivity higher than 88% (Table 2).
In agreement with homogeneous result, (E)-vinylboronate was
obtained as the main product resulting from an anti-Markonikov
and syn-addition of the pinacol borane.
2.4. Phenylacetylene hydroboration in the presence of phosphine
In a 15 mL reaction tube, under argon, containing the M@OS
(0.1 mol%) and the selected phosphine (1 mol%) were added pina-
colborane (1.0 mmol) and then phenylacetylene (1.0 mmol). The
mixture was stirred at 85 ◦C for 23 h. The reaction mixture was
then diluted in dichloromethane and filtrated over a pad of silica.
After washing twice with 10 mL of dichloromethane the filtrate was
concentrated under vacuum to give the corresponding vinylborane
as a mixture of isomers. Product distribution was determined by
GC/MS. Conversion is determined using the relative areas in GC/MS
and according to mesitylene as internal standard. The spectral data
were in agreement with those reported in the literature.
(E)-2-Phenylethenylboronic acid pinacol ester (ˇ-trans-3): [14] 1
H
NMR (300 MHz, CDCl3) ı 7.53–7.42 (m, 2H), 7.44–7.27 (m, 4H), 6.17
(d, 1H, J = 18.4 Hz), 1.32 (s, 12H); MS (EI) tR = 9.07 min; m/z: 105.1
(26%), 130.1 (100%), 144.1 (63%), 215.1 (22%), 230.1 (M+, 43%).
(Z)-2-Phenylethenylboronic acid pinacol ester (ˇ-cis-3): [15] 1H
NMR (300 MHz, CDCl3) ı 7.56–7.45 (m, 2H), 7.40–7.22 (m, 4H), 5.59
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O
O
M@OS (0.1 mol%)
85°C, 23h
O
O
2
O
B
O
B
Ph
H B
O
B
Ph
O
Ph
Ph
1
α-3
β-cis-3
β-trans-3
(1 equiv.)
(1 equiv.)
Scheme 2. Reaction conditions for terminal alkyne hydroboration catalyzed by M@OS NCs.
Fig. 2. TEM images of the Pt NCs stabilized by 4 OSs: Pt@TBAB (a), Pt@BnNMe3Br (b), Pt@CTAB (c) and Pt@CTANTf2 (d) with NCs high resolution image (e) and surface area
electron diffractions (SAED) image corresponding to Pt@TBAB (f).
Encouraged by these preliminary results we prepared and evalu-
ated the others metal systems, namely platinum (Fig. 2), ruthenium
or iridium (Fig. 3) M@OS. Using the same stabilizers and a different
metal it was assessed not only the catalytic efficiency of those new
NCs, but also the morphology tuning. We clearly notice a size vari-
ation and different dispersion profiles, revealing thus a disparity in
precursor decomposition kinetics and nucleation/growth regime
but in the same time maintaining the high cristallinity of the pre-
pared material.
As can be seen in TEM images (Fig. 3) nanocrystals organiza-
tion/dispersion is influenced by the metal nature and NCs surface
chemistry. Indeed, well dispersed NCs were obtained for Ru, more
agglomerated ones for Pt and Rh, and aggregated for Ir. These obser-
vations match the catalytic activities of M@OS. Platinum based NCs
led to similar reactivity with rhodium (Table 2). Indeed M@TBAB
afforded great conversion. However, 8–9% of ␣ isomer was also
formed (Table 2). Symmetrical and low melting point TBAB led to
bulkier stabilization and formation of a dense and compact shell
around metal core (Fig. 2a). This prevented incoming metal atoms
to attach to the nuclei, impeding the growth and maintaining small
NCs size. On the contrary, dissymmetrical OS, as CTAB and BnTAB,
has favored the NCs growth. The organization and long chain flex-
ibility of CTAB could behave as a liquid crystal,[17] increasing the
mobility of the 12-C alkyl chain around the metal core, allowing
thus a higher metal atom movement along the metal nuclei and h
resulting in a higher growth. However by using a more hindered
counter anion as triflimide, sustain a more compact shell around
the metal core (similar with TBAB) and clearly limit the NCs growth
resulting NCs around 2 nm (Fig. 2 and 3).
Table 2
Phenylacetylene hydroboration using the hybrid systems M@OS with their corre-
sponding product distribution.
Entry
M@OS
˛-3
ˇ-cis-3
ˇ-trans-3
Conv. (%)
1
2
3
4
Rh@TBAB
Rh@[BnNMe3]Br
Rh@CTAB
9
1
3
1
3
0
1
0
88
99
96
99
99
76
92
85
Rh@CTANTf2
5
6
7
8
Pt@TBAB
Pt@[BnNMe3]Br
Pt@CTAB
8
5
2
1
4
0
0
1
88
95
98
98
92
83
67
87
Pt@CTANTf2
9
10
11
12
Ir@TBAB
Ir@[BnNMe3]Br
Ir@CTAB
11
18
8
2
4
4
2
87
78
88
82
100
57
71
Ir@CTANTf2
16
72
13
14
15
16
Ru@TBAB
Ru@[BnNMe3]Br
Ru@CTAB
1
0
1
0
0
0
0
0
99
>99
99
93
71
68
59
Ru@CTANTf2
>99
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Fig. 3. TEM images of the Ir NCs stabilized by 4 OSs: Ir@TBAB (a), Ir@BnTAB (b), Ir@CTAB (c) and Ir@CTANTf2 (d); TEM images of the Ru NCs for the same OSs: Ru@TBAB (e),
Ru@BnTAB (f), Ru@CTAB (g) and Ru@CTANTf2 (h) and NCs sizes were obtained from a Gaussian distribution by counting more than 150 NCs.
3.2. Catalyst behavior
for Pt@OS hydroboration. More surprisingly Ir@OS NCs gave the
lower selectivity as a mixture of ˇ-trans-3 and 8–18% of ˛-3
compound. The dispersion of the hybrid nanocrystals obviously
influenced their efficiency, very clearly exemplified with Ir@BnTAB
Prepared M@OS were then tested in hydroboration. CTANTf2
allowed a compromise between yield (85%) and selectivity (98%)
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Scheme 3. Hydroboration catalyzed by Ir@CTANTf2 in the presence of phosphine.
and Ir@TBAB systems (Fig. 3b and a). The Ir@BnTAB NCs with its low
monodispersity gave one of the lowest conversions, while Ir@TBAB
NCs with similar size but an excellent dispersion was found to be
the best catalyst.
Acknowledgement
The authors want to acknowledge the financial support of the
Aquitaine Region and the ANR-12-CDII-010-NANOCAUSYS.
Using Ru@OS system (Fig. 3e-h), we were pleased to observe
that selectivity exceeded 99% of ˇ-trans-3. However, the conversion
was decreased according to OS steric hindrance. As expected, the
agglomerated Ru@CTANTf2 (Fig. 3h) led to a lower conversion.
Our further investigations were focused on the addition of dif-
ferent ligands to tune the nanocatalysts reactivity. The common
used ligands, such as triphenylphosphine or tricyclohexylphospine
are already known for their performance in homogeneous cataly-
sis for the same hydroboration. Combined with Rh(I) catalyst, they
led to a reverse selectivity affording mainly the (Z)-isomers [3b,18].
With Ir@CTANTf2, in the presence of 1 mol% of phosphine, selectiv-
ity (up to 97–98%) and conversion (87%) were improved (Scheme 3).
These experiments demonstrate not only the facile metal surface
modulation, but also the non-negligible role of its surface proper-
ties. The design and preparation of highly active new catalyst with
surface properties modulation by the ligand type and ligand ratio,
is under investigation, and some preliminary results were reported
in our previous work [19].
References
[1] K. Burgess, M.J. Ohlmeyer, Chem. Rev. 91 (1991) 1179–1191.
[2] (a) X. Zeng, Chem. Rev. 113 (2013) 6864–6900;
(b) I. Beletskaya, C. Moberg, Chem. Rev. 106 (2006) 2320–2354;
(c) I. Beletskaya, A. Pelter, Tetrahedron 53 (1997) 4957–5026.
[3] (a) Y. Yamamoto, R. Fujikawa, T. Umemoto, N. Miyaura, Tetrahedron 60 (2004)
10695–10700;
(b) T. Ohmura, Y. Yamamoto, N. Miyaura, J. Am. Chem. Soc. 122 (2000)
4990–4991;
(c) S. Pereira, M. Srebnik, Tetrahedron Lett. 37 (1996) 3283–3286.
[4] X. He, J.F. Hartwig, J. Am. Chem. Soc. 118 (1996) 1696–1702.
[5] J.J.J. Juliette, D. Rutherford, I.T. Horváth, J.A. Gladysz, J. Am. Chem. Soc. 121
(1999) 2696–2704.
[6] A.M. Segarra, R. Guerrero, C. Claver, E. Fernández, Chem. Eur. J. 9 (2003)
191–200.
[7] J. Zhao, Z. Niu, H. Fu, Y. Li, Chem. Commun. 50 (2014) 2058–2060.
[8] J. Ramírez, M. Sanaú, E. Fernández, Angew. Chem. 120 (2008) 5272–5275.
[9] Y. Zhu, S.H.A. Jang, Y.H. Tham, O.B. Algin, J.A. Maguire, N.S. Hosmane,
Organometallics 31 (2012) 2589–2596.
[10] F. Hassine, M. Pucheault, M. Vaultier, C. R. Chim. 14 (2011) 671–679.
[11] H.D.S. Guerrand, L.D. Marciasini, T. Gendrineau, O. Pascu, S. Marre, S. Pinet,
M. Vaultier, K. Jensen, C. Aymonier, M. Pucheault, Tetrahedron 70 (2014)
6156–6161.
[12] O. Pascu, V. Liautard, M. Vaultier, M. Pucheault, C. Aymonier, RSC Adv. 4 (2014)
59953–59960.
4. Conclusions
We reported the efficient, economic and green hydrobora-
tion using an authentic nanocatalyst design. Our green approach,
based on scCO2 assisted synthesis of highly active transition
metal nanocatalysts stabilized by onium salt, affords ready-to-use,
clean, air and moisture stable powder. The as prepared advanced
organic/inorganic hybrids NCs were successfully used in the regio-
and stereoselective hydroboration of alkynes. By varying the metal
and/or the onium salt stabilizer we study the NCs morphology and
surface properties. Altering the large surface of the NCs using cat-
alytic amount of small phosphines manage to improve the M@OS
NCs selectivities. Recycling tests by simple M@OS precipitation and
extraction led to decrease in activity. This work emphasizes the
importance of fine tuning the surface properties to achieve good
selectivities and conversion in the aim of obtaining an efficient
heterogeneous catalyst.
[13] (a) F. Cansell, C. Aymonier, J. Supercrit. Fluids 47 (2009) 508–516;
(b) S.E. Bozbag, D. Sanli, C. Erkey, J. Mater. Sci. 47 (2012) 3469–3492.
[14] (a) N. Selander, B. Willy, K.J. Szabó, Angew. Chem. Int. Ed. 49 (2010)
4051–4053;
(b) A. Grirrane, A. Corma, H. Garcia, Chem. Eur. J. 17 (2011) 2467–2478;
(c) V. Hickmann, A. Kondoh, B. Gabor, M. Alcarazo, A. Fürstner, J. Am. Chem.
Soc. 133 (2011) 13471–13480.
[15] G.A. Molander, N.M. Ellis, J. Org. Chem. 73 (2008) 6841–6844.
[16] J.W. Clary, T.J. Rettenmaier, R. Snelling, W. Bryks, J. Banwell, W.T. Wipke, B.
Singaram, J. Org. Chem. 76 (2011) 9602–9610.
[17] (a) A.M. Scurto, E. Newton, R.R. Weikel, L. Draucker, J. Hallett, C.L. Liotta, W.
Leitner, C.A. Eckert, Ind. Eng. Chem. Res. 47 (2007) 493–501;
(b) S.G. Kazarian, N. Sakellarios, C.M. Gordon, Chem. Commun. (2002)
1314–1315.
[18] J. Cid, J.J. Carbó, E. Fernández, Chem. Eur. J. 18 (2012) 1512–1521.
[19] (a) T. Gendrineau, S. Marre, M. Vaultier, M. Pucheault, C. Aymonier, Angew.
Chem. Int. Ed. 51 (2012) 8525–8528;
(b) O. Pascu, L. Marciasini, S. Marre, M. Vaultier, M. Pucheault, C. Aymonier,
Nanoscale 5 (2013) 12425–12431.
Please cite this article in press as: V. Liautard, et al., Advanced nanostructured catalysts for hydroboration, Catal. Today (2015),
http://dx.doi.org/10.1016/j.cattod.2014.11.038