Simpler and Cleaner Synthesis of Variously Capped Cobalt Nanocrystals Applied in the Semihydrogenation of Alkynes

Article abstract of DOI:10.1021/acs.inorgchem.0c01641

Unlike the classical organometallic approach, we report here a synthetic pathway requiring no reducing sources or heating to produce homogeneous hexagonal-close-packed cobalt nanocrystals (Co NCs). Involving a disproportionation process, this simple and fast (6 min) synthesis is performed at room temperature in the presence of ecofriendly fatty alcohols to passivate Co NCs. Through a recycling step, the yield of Co NCs is improved and the waste generation is limited, making this synthetic route cleaner. After an easy exchange of the capping ligands, we applied them as unsupported catalysts in the stereoselective semihydrogenation of alkynes.

Full text of DOI:10.1021/acs.inorgchem.0c01641

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Simpler and Cleaner Synthesis of Variously Capped Cobalt
Nanocrystals Applied in the Semihydrogenation of Alkynes
A. Sodreau, A. Vivien, A. Moisset, C. Salzemann, C. Petit,* and M. Petit*
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ABSTRACT: Unlike the classical organometallic approach, we
report here a synthetic pathway requiring no reducing sources or
heating to produce homogeneous hexagonal-close-packed cobalt
nanocrystals (Co NCs). Involving a disproportionation process,
this simple and fast (6 min) synthesis is performed at room
temperature in the presence of ecofriendly fatty alcohols to
passivate Co NCs. Through a recycling step, the yield of Co NCs is
improved and the waste generation is limited, making this synthetic route cleaner. After an easy exchange of the capping ligands, we
applied them as unsupported catalysts in the stereoselective semihydrogenation of alkynes.
Scheme 1. Previous Pathways to Synthesize Co Nanoobjects
(AOT = Dioctyl Sulfosuccinate)
INTRODUCTION
■
Nowadays, the formation of well-defined nanoparticles (NPs)
can be considered to be common. Indeed, countless syntheses
have been published over the past 20 years,1 increasing the
morphological control and originality of the nanoobjects
formed.2 This new nanometric organization makes cobalt (Co)
NPs appear as promising materials with potential magnetic,3
electronic,4 and catalytic5 applications. The chemical route
highly contributed to this progress and allowed high control of
their structural homogeneity (shape, size, and crystallinity), a
crucial point to improving their performance.6 For instance,
compared to the two other crystalline phases accessible for Co
NPs [ε and face-centered cubic (fcc)], the hexagonal-close-
packed (hcp)-Co structure is acclaimed in catalysis.7
Experimental observations show that the Fischer−Tropsch
reaction was better performed by a hcp-Co catalyst.8
This approach provided efficient ways to synthesize
homogeneous Co NPs using Co salts or organometallic
complexes as starting materials.9 In Scheme 1, we summarize
remarkable strategies allowing one to synthesize a wide range
of Co nanoobjects (spheres, rods, wires, disks, etc.). The
reverse-micelle strategy generates nanospheres at room
temperature (RT) by a microemulsion of water in oil. The
reduction of Co salts was carried out with sodium borohydride
(NaBH4), resulting in an undesirable formation of additional
Co2B NPs10 (Scheme 1a). The polyol method has the
advantage of using the polyol itself as a solvent and reducing
agent but requires high temperature to induce the reduction
process.11 Well-defined nanorods or platelets can be obtained
through a nucleating agent (ruthenium or iridium seeds;
Scheme 1b). Via hot injection of the cobalt(0) complex
Co2CO8, Alivisatos et al. induced its thermolysis and the
formation of nanodisks in only few seconds. However, a
mixture of crystalline phases was observed, and pure hcp-Co
NPs remained difficult to isolate12 (Scheme 1c). A shape
control was performed by Chaudret’s group using [Co(η3-
C8H13)(η4-C8H12)], giving spheres and rods after respectively
3 and 48 h (wires were also accessible with another ligand
mixture in 48 h). Nevertheless, 3 bar of H2 pressure is required
to reduce this cobalt(I) complex13 (Scheme 1d). More
recently, the same group developed a new route involving
Co{N(SiMe3)2}2 to achieve polymorphismic nanoobjects with
variable crystalline structure, but a reductive atmosphere and 2
Received: June 3, 2020
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days at 150 °C were required. A major drawback here is the
synthesis and storage of the starting material14 (Scheme 1e).
These syntheses need specific synthetic conditions like high
temperature, reductive atmosphere, and/or additional reagents
(reductants, nucleation seeds, etc.). Some of them also
required a long reaction time of up to 2 days. In addition,
some solvents and reagents involved in these syntheses can
cause pollution and safety issues (toxic or explosive gases, high
temperature, polluting waste, etc.). Moreover, the obtention of
spherical hcp-Co NPs with size control is still challenging and
mandatory for catalytic applications. Consequently, the
development of a synthetic strategy presenting faster, cleaner,
and less energetic conditions appears as a key point to move
further.15 More generally, safer and ecofriendly reagents and
conditions appear more and more mandatory.
The disproportionation process is a fairly old reaction
described by Gadolin in 1788 on tin.16 This redox pathway was
used to synthesize gold17 and copper18 NPs. In the case of
copper, fine morphological control is obtained using
thermodynamic or kinetic conditions.18b In 2016, we extended
this pathway to Co by the formation of hcp-Co nanospheres
and nanorods in oleylamine (OAm) at 190 °C.19
In this context, it seems interesting to us to optimize this
original process to synthesize Co NPs under the mildest
conditions. Herein, we report the synthesis of homogeneous
hcp-Co nanocrystals (NCs) at RT in just 6 min, implying a
disproportionation pathway in which no reductive agents are
necessary. Moreover, the capping of generated NPs is
performed by biosourced fatty alcohol ligands, which is
unusual for Co NPs but previously observed for other
transition-metal NPs.20 In addition, through a recycling
process, most of the waste can be reused for synthesis of the
starting Co complex. Finally, we tested the catalytic activity of
these Co NPs in a preliminary study on the semihydrogenation
of alkynes.
Table 1. Synthesis of NPs by [ClCo(PPh3)3]
Disproportionation in THF at RT
a
entry
1
ligand
none
amount/equiv
time
observations
3 min
black magnetic powder +
blue supernatant
2
3
4
5
6
7
8
9
oleylamine
diglyme
diglyme
dioctyl ether
dioctyl ether
tridecanol
tridecanol
tridecanol
tridecanol
5
5
1
5
1
10
5
3
24 h
NPs, d = 1.1 0.6 nm
7 min
3 min
8 min
3 min
polydisperse-sized NPs,
heterogeneous shape
polydisperse-sized NPs,
heterogeneous shape
15 min no homogeneous shape
9 min
6 min
30 min
spherical NPs, = 8.7
0.6 nm (7%),
homogenous shape
and size
10
3
11
12
octanol
octadecanol
3
3
4 min
4 min
no homogeneous shape
homogenous shape and
size, d = 8.6 0.5 nm
a
All TEM pictures are available in Table S1.
isolated (see the Supporting Information for the disproportio-
nation mechanism).19,23 Once generated, it rapidly degraded as
metallic Co and free triphenylphosphine. In order to control
the growth of these resulting Co nuclei, a wide range of ligands
were tested (Table 1).
The first ligand we tested was OAm, a common fatty amine
for capping NPs. With the addition of 5 equiv of OAm, only
small polydispersed Co NPs were collected and the reaction
time was greatly increased (Table 1, entry 2). This can be
explained by ligand exchange on the starting complex between
triphenylphosphine and OAm, resulting in inhibition of the
THF effect. Then, other ligands were tested having
coordination properties closer to those of THF. With ether
ligands, the redox reaction occurred in 10 min or less.
However, the NPs isolated have random shape and size (Table
1, entries 3−6). In the presence of 5 equiv of tridecanol, a fatty
alcohol, NPs presenting homogeneous shape and size can be
easily collected in only 9 min (Table 1, entry 8). Variable
amounts of tridecanol were tested to improve the reaction.
With only 3 equiv of tridecanol, the results were similar but the
reaction time decreased to 6 min (Table 1, entry 9).
Interestingly, no morphological changes were observed over
the time (Table 1, entry 9 vs 10). Nevertheless, beyond 10
equiv of tridecanol, the reaction time increased and shape
control was lost (Table 1, entry 7). Other alcohols have been
tested: (i) with a smaller alkyl chain such as octanol, the NPs
formed were not well-defined (Table 1, entry 11); (ii) with a
longer alkyl chain such as octadecanol (stearyl alcohol), similar
NPs were collected (Table 1, entry 12). Stearyl alcohol is
interesting as a cheaper and innocuous alternative to
tridecanol. Among all of these tests, 3 equiv of tridecanol (or
octadecanol) can be considered to be optimal conditions.
After ethanol (EtOH) treatment, the transmssion electron
microscopy (TEM) pictures show spherical NPs with an
average size of 8.7 0.6 nm and a very small polydispersity
(7%; Figure 1a). IR and scanning electron microscopy
(SEM)−energy-dispersive X-ray (EDX) show mainly the
presence of fatty alcohols, traces of chlorine, and no
triphenylphosphine (see the Supporting Information). As we
have shown in our previous approach,23 the halide present on
the starting complex has a significant importance in the kinetics
of the disproportionation process. Indeed, with heavier halide
derivatives, bromine and iodide, the reaction time increases up
RESULTS AND DISCUSSION
■
Recently, Nocera et al. were able to generate H2 from HCl
using [ClNi(PPh3)3] as the catalyst.21 Interestingly, the
proposal mechanism suggests as the first catalytic step a
disproportionation of this nickel(I) complex in tetrahydrofuran
(THF) at RT. In an older publication, Gosser described the
formation of a “black magnetic powder” when [ClCo(P-
(OPh)3)3] was dissolved in acetonitrile (MeCN) at 45 °C and
also concluded in a disproportionation process.22 In these two
examples, interactions between each complex and its respective
solvent are likely involved. Probably, a solvent−phosphine
exchange is capable of inducing this redox process. Indeed,
MeCN and THF are known to be coordinated solvents, and
several examples present organometallic complexes coordi-
nated by them.
Thus, in our experiments, once [ClCo(PPh3)3] was
dissolved in THF, a black precipitate stuck to the magnetic
stirring bar and a blue supernatant was quickly observed at RT
(Table 1, entry 1). This blue color is characteristic of the
[Cl2Co(PPh3)2] complex, suggesting a disproportionation
process. Moreover, the ongoing monitoring of the color of
the solution allows an estimation of the end of the reaction.
Initially brown, it quickly changed to black with emerald green
reflections, and when it turned night blue, the reaction could
be considered finished. It is assumed that this redox process
generates [Co(PPh3)4] and [Cl2Co(PPh3)2] in a 50:50 ratio
from [ClCo(PPh3)3]. However, [Co(PPh3)4] has never been
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phosphine, or phosphine oxide (see the Supporting Informa-
tion).
In order to fully characterize the structures of these 8.7 nm
Co NCs, microscopic and macroscopic analyses were
performed (Figure 3). Electron diffraction collected by TEM
Figure 1. Synthesis of hcp-Co NCs from (a) [ClCo(PPh3)3], (b)
[BrCo(PPh3)3], and (c) [ICo(PPh3)3] complexes with 3 equiv of
tridecanol in THF in respectively 6, 12, and 45 min at RT. (d)
Evolution of the size of the NPs with the cobalt(I) complex used as
the starting material.
12 and 45 min, respectively (Figure 1b,c). This affects the size
of the NPs, which decrease according to the atomic number of
the halide, from 8.7 0.6 nm for chloride to 2.7 0.4 nm for
iodide (Figure 1d).
Once isolated, the NPs can be redispersed in a solution of 20
equiv of OAm in toluene. Thereby, ligand exchange between a
fatty alcohol and OAm was carried out. OAm is a classic NP
surfactant known to generate 2D and 3D organization.1a After
treatment, this exchange was monitored by TEM (Figure 2).
We also demonstrated that a partial or total ligand exchange
could be realized with other chemical functions such as acid,
Figure 3. (a) HRTEM pictures of the 8.7 nm Co NCs stabilized by a
fatty alcohol. (b) Zoom on one isolated Co NC. (c) FT of this Co
NC. (d) Electron diffraction from TEM of similar NPs. (e) XRD of
Co NC powder.
exhibits several rings showing the presence of a crystalline
structure. After size measurement, the reticular distances
corresponded to the (100), (002), (101), (102), (110), (103),
(200), and (112) crystalline planes of the hcp crystalline phase
(Figure 3d). This phase was confirmed by high-resolution
TEM (HRTEM) with the presence of similar distances found
by Fourier transform (FT) corresponding to the (100), (002),
and (101) planes (Figure 3a−c). X-ray diffraction (XRD)
analysis performed on NP powder shows a set of fine peaks at
18.9°, 20.1°, 21.2°, 32.8°, 34.4°, 38.2°, and 38.7° correspond-
ing to a hcp-Co crystalline structure (Figure 3e).
Scherrer’s calculation was applied to the peak at 32.8°, giving
a crystallite size of approximately 8 nm matching with the size
of the NPs. All reticular distances and their corresponding
planes of these analyses are summarized in Table 2.
Nevertheless, broad peaks at 15°, 16.3°, and 27° were also
observed and correspond to the Co3O4 crystalline structure.
Scherrer’s calculation applied to these peaks gives a crystallite
size of smaller than 1 nm, likely resulting from an oxidized
shell. This oxidation can be explained by the weakness of fatty
alcohol as a chelating ligand. Interestingly, no oxidative layer is
visible by microscopic analyses, so we cannot exclude possible
oxidation during the sample preparation.
In the literature, Alivisatos et al.12a and Cheon et al.24 have
shown that the hot injection of Co2(CO)8 at 180 °C gives Co
NCs. After a rapid cooling and short reaction time (kinetic
conditions), Alivisatos et al. observed a mixture of hcp-Co and
Figure 2. (a) Co NPs after ligand exchange with OAm and (b) Co
NPs capped by OAm and organized in two and three dimensions. (c)
Size distribution of Co NPs.
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netic behavior as described by Zhang et al. with other hcp-Co
NPs (0.16 T at 3 K and 0.05 T at 300 K).27
We also reported zero-field-cooled/field-cooled (ZFC/FC)
measurement (Figure 5). First, a peak was observed on the
Table 2. Theoretical Reticular Distances for Bulk hcp-Co
and Experimental Reticular Distances Obtained by XRD,
TEM, and HRTEM
a
dhkl
h
k
l
(hcp) theorical
XRD
2.16
2.03
1.92
e-diff by TEM HRTEM
1
0
1
1
1
1
2
1
0
0
0
0
1
0
0
1
0
2
1
2
0
3
0
2
2.171
2.025
1.916
1.485
1.254
1.150
1.086
1.067
2.21
2.07
1.93
1.54
1.27
1.17
1.09
1.06
2.14
2.05
1.91
1.25
1.19
1.08
1,07
a
All data are in angstroms.
ε-Co. When the time of the reaction increased to minutes
(thermodynamic conditions), only a pure ε-Co phase was
synthesized. However, under kinetic conditions, they specified
that the mixture was mainly composed of hcp-Co, and ε-Co
was due to too slow cooling of the medium. Still under kinetic
conditions (110 °C and 5 s), Cheon et al. also observed a
mixture of the crystalline structure, with a major fcc phase and
a minor hcp phase. However, when the temperature increased
Figure 5. Magnetization curves at 3 and 300 K of 8.7 nm spherical Co
NCs in solution with an EtOH quench.
ZFC curve at 10 K. This may be due to traces of oxide
previously mentioned after XRD analysis. Second, no overlap
of the ZFC and FC curves was observed below 350 K.
Consequently, the blocking temperature TB (transition
temperature between the superparamagnetic and ferromag-
netic fields) was not reached at 350 K. Theoretically, TB is
estimated at 410 K for NPs with d ∼ 8.7 nm (magnetic
anisotropic constant of hcp-Co = 4.1 × 105 J m−3), explaining
the ferromagnetic behavior observed at RT. Interestingly, 8 nm
Co NPs synthesized by Legrand et al. with a fcc structure
present a lower TB at only 85 K, for nonisolated NPs.28 Such
an observation confirms the hcp structure of these NPs.
As mentioned, this redox pathway generates a maximum of
50% [Co(PPh3)4], inducing an expected yield of 50%. This can
be considered to be a major drawback in the development of
this synthetic route. Nevertheless, after calcination of stabilized
Co NPs, only 42 mol % of the Co introduced is contained in
the NPs. Moreover, after EtOH treatment, the NPs are easily
separated from the solution of [Cl2Co(PPh3)2] and free
triphenylphosphine, which can be recycled in [ClCo(PPh3)3]
by the addition of NaBH4 with a yield of 76%. Thus, on the
basis of the recovered starting material, the yield of the
reaction is 86% (Scheme 2), and after two recycling runs, the
yield of isolated NPs increases up to 68%.
to 180 °C, hcp nanorods were observed. de la Pena O’Shea et
̃
al. mentioned that the hcp phase is more stable at RT and
ambient pressure at the bulk scale.25 In our case, the
disproportionation process allows synthesis at RT in 6 min
and only the hcp-Co phase is observed, which is consistent
with kinetic conditions, while usually the fcc-Co phase is
obtained under thermodynamic conditions for NPs below 20
nm.26
This structural organization possesses higher anisotropy,
improving the magnetic performance of these objects.24
Therefore, the Co NC magnetic behavior was monitored by
vibrating-sample magnetometry (VSM). Their magnetization
cycle was performed at 3 and 300 K, and we focus our
attention on the coercity field (Figure 4). It decreased with the
temperature from 0.17 to 0.03 T respectively at 3 and 300 K,
but at both temperatures, an open hysteresis loop was clearly
observed. Thus, observations are consistent with a ferromag-
A recent publication estimated that a quarter of chemical
transformations involve at least one hydrogenation step.29a In
this context, NPs are more and more applied in catalytic
hydrogenation, taking advantage of their large specific surface
due to a high surface/volume ratio.29b Therefore, the
Scheme 2. Synthesis of NPs via a Disproportionation
Pathway at RT and Recyclability of the Cobalt(II) Complex
in the Starting Material
Figure 4. ZFC/FC curve obtained for 8.7 nm spherical Co NCs in
solution with an EtOH quench.
D
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development of easily synthesized Co NPs emerges as a
promising pathway to access to the hydrogenation catalyst. In
the specific case of the semihydrogenation of alkynes, a wide
range of transition metals have been studied especially
palladium, gold, and platinum.29a,c Huge efforts have been
made for understanding the selectivity and mechanism of the
reaction. However, their cost and sustainability required the
use of cheaper transition metals.30 For Co, only one example
has been published (by Beller’s group) using supported Co
NPs as the catalyst.5a We focus our attention on the
semihydrogenation of diphenylacetylene (DPA) using un-
supported hcp-Co NPs as the catalyst. The catalytic experi-
ments were performed under H2 pressure and heated in an
autoclave. All different conditions tested are given in Table 3.
Table 4. Unsupported Co NPs Catalyzed the
Semihydrogenation of Various Alkynes
entry
R1
R2
convn/% ratio E/Z alkane/%
1
2
3
4
5
Ph
4-Br-Ph
4-Bu-Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-Br-Ph
4-Bu-Ph
SiMe3
CH2OH
CH2OH
CH(OH)CH3
CO2Et
99
80
81
24
99
20
88
68
76
1:99
6:94
17
11
4
19:81
17:83
100:0
10:90
100:0
100:0
11:89
90
a
6
7
8
9
68
37
Table 3. Unsupported Co NPs Catalyzed the
Semihydrogenation of DPA
C(CH3)2OH
C(CH3)2OH
a
Under 0.2 MPa of H2 pressure.
the reduction of simple alkynes with Co/Pt NPs.31 They
showed that when the alkyne competes with a stabilizing
ligand, overreduction is favored. The E selectivity in our result
is due to overreduction of the Z isomer. Indeed, the same
reaction under a lower pressure drives no overreduction, and Z
isomer is now the major product with a ratio 1:9 (Table 4,
entry 6). To avoid chelation of the alcohol on the surface, we
ran an experiment with the bulkier bis(isopropyl alcohol)-
substituted acetylene. We observed a selectivity in favor of the
Z isomer like with DPA and, more importantly, no over-
reduction (Table 4, entry 8).
b
entry T/°C t/h H2 pressure/bar convn/% ratio E/Z
alkane/%
c
1
2
3
4
5
6
120
120
120
120
RT
RT
16
16
16
1
16
72
30
20
10
30
30
30
99
99
90
99
10
58
1:99
5:95
1:99
4:96
4:96
5:95
17
15
7
3
traces
6
a
Reaction conditions: 0.5 mmol of DPA in 2 mL of toluene
containing 5 mol % of Co NPs capped by OAm. The ratio of Z/E is
determined by NMR. Beller’s hydrogenation conditions.
b
c
CONCLUSION
■
We describe here a RT expeditious synthesis of hcp-Co NCs
based on a disproportionation process. Mixing [ClCo(PPh3)3]
with a fatty alcohol as the stabilizing ligand in THF led to
homogeneous Co NPs in 6 min. When the halide substituent
on the complex is played with, the NPs size can be varied from
2.7 to 8.7 nm. These Co NPs have been fully characterized by
XRD, TEM, HRTEM, and VSM and exhibit a hcp crystalline
structure consistent with the synthetic conditions (kinetic
conditions). Furthermore, initially at 42%, the yield was
improved by recycling byproducts. Compared to the previous
syntheses published, this synthesis proposes a cleaner and less
energetic pathway. Ligand exchange to OAm allowed 2D and
3D organization and provided efficient Co NPs for the catalytic
semihydrogenation of alkynes. Primary catalytic tests show
high conversion and an interesting selectivity, with inversion of
the ratio E/Z following the chelating properties of the
substrate.
For all of the conditions tested, the E/Z ratio shows the Z
isomer as the major product with high selectivity. The
temperature of the reaction appears to be important. Indeed,
at 120 °C after 16 h, 90% conversion can be reached, whereas
only 10% is observed at RT (Table 3, entry 1 vs 5). However,
increasing the reaction time at RT to 72 h allows one to reach
58% conversion (Table 3, entry 6). It is noteworthy to
mention that overreduction to alkane is observed at 120 °C
when the 1 h reaction is compared with the 16 h reaction, with
no change of the selectivity (Table 3, entry 1 vs 4). Reducing
the H2 pressure resulted in less alkane formation but lower
conversion (Table 3, entries 1−3). We thus considered the
conditions of entry 1 for extension to other alkynes because
they give the highest conversion and ratio E/Z (in this case,
the selectivity is higher than that observed by Beller et al.).
Similar selectivity is obtained with 4,4′-dibromodiphenyla-
cetylene with good conversion (Table 4, entry 2). However,
with electron-donating groups such as n-butyl in the para
position, formation of the E isomer is higher, with 80%
conversion (Table 4, entry 3). Unsymmetrical alkynes can also
be reduced. The presence of a bulky group such as
tetramethylsilane is tolerated with similar selectivity, but
lower conversion is observed (Table 4, entry 4). Surprisingly,
when the alkynes bear an alcohol or an ester substituent (Table
4, entries 5, 7, and 8), only the E isomer is observed, together
with the formation of an important amount of alkane. A
possible explanation for the overreduction can be that the
presence of a chelating oxygen group at the propargyl position
allows the molecule to stay at the surface of the NPs.
Shevshenko et al. already observed these kinds of results for
EXPERIMENTAL SECTION
■
General Procedure for the Synthesis of X(PPh3)3Co
Complexes. To CoX2·6H2O (40 mmol) and triphenylphosphine
(122 mmol) was added 600 mL of degassed EtOH. The resulting
heterogeneous solution was stirred vigorously at 60 °C for 30 min to
form in situ the complex X2(PPh3)2CoII as a bright-blue powder. The
mixture was then cooled to 30 °C, and NaBH4 (34 mmol) were added
in 10 portions every 10 min. The color of the mixture changed from
bright blue to dark brown. After 2 h, the brown precipitate was
filtered, washed sequentially with EtOH and diethyl ether (Et2O), and
finally dried under vacuum to give 25 g of the desired [XCo(PPh3)3]
complex in 76% yield.
Synthesis of hcp-Co NCs. A total of 132 mg of [ClCo(PPh3)3]
(0.15 mmol) was loaded into a screw-capped tube of 12 mL with a
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magnetic bar. In another tube, 90 mg of tridecanol (0,45 mmol) was
dissolved in 6 mL of THF. Then, the solution of tridecanol was
poured onto [ClCo(PPh3)3] under magnetic stirring. The solution
changed quickly from brown to black. After 6 min, about 15 mL of
EtOH was added to the black solution and centrifuged at 2500 rpm
for 5 min. A black powder was observed at the bottom of the tube
with a blue supernatant. After elimination of the supernatant, the NPs
were dispersed in 2 mL of toluene and a drop was laid on a copper
TEM grid to perform microscopic characterization. NPs from
[BrCo(PPh3)3] and [ICo(PPh3)3] were prepared with the same
procedure and amount as that for the [ClCo(PPh3)3] precursor.
Recycling Procedure. After 10 standard reactions, all super-
natants were collected, transferred to a Schlenk tube, and dried. Then,
under argon, 50 mL of degassed EtOH was added and 26 mg of
NaBH4 (0.9 equiv) was introduced in portions over 30 min under
vigorous stirring. After 4 h at RT, the dark-brown solid formed was
filtered and washed three times with EtOH and finally once with
Et2O. The solid was then dried, giving 490 mg (76%) of
[ClCo(PPh3)3].
Ligand-Exchange Procedure. To a dispersed solution of NPs in
toluene was added 20 equiv of OAm, and the resulting solution was
mixed for 5 min. The excess of ligands was removed by a EtOH
washing (20 mL).
Catalytic Test. Under an argon atmosphere, in a sealed tube was
added 0.5 mmol of the substrate with 2 mL of a toluene suspension
containing 5 mol % of Co NPs passivated by OAm. Then the tube
was introduced to an autoclave and filled with the desired pressure of
H2. The mixture was stirred and heated in an oil bath. At the end of
the reaction, the solution was filtered over silica and washed with
pentane or ethyl acetate (depending on the polarity of the substrate).
The solvent was removed under reduced pressure to give the desired
compound.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
This work was financially supported by Sorbonne Universite,
CNRS, and the ANR program under reference NUMEN ANR-
17-CE09-0037. The authors thank Sandra Casale (LRS, UMR
́
7197, Sorbonne Universite, CNRS) for her help with the
microscopic characterization. We also gratefully acknowledge
Mohamed Selmane (LCMCP, UMR 7574, Sorbonne Uni-
versite, CNRS, College de France) for his contribution to the
XRD analysis. Celine Paris (MONARIS, UMR 8233, Sorbonne
Universite, CNRS) is also acknowledged for her help with the
IR analysis.
́
̀
́
́
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ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01641.
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■
Corresponding Authors
́
C. Petit − Sorbonne Universite, MONARIS, UMR 8233, 75005
Paris, France; orcid.org/0000-0003-3206-0246;
Email: christophe.petit@sorbonne-universite.fr
́
M. Petit − Sorbonne Universite, CNRS, Institut Parisien de
́
Chimie Moleculaire, UMR 8232, 75005 Paris, France;
́
Estrader, M.; Berliet, A.; Maury, S.; Fecant, A.; Chaudret, B.; Serp, P.;
orcid.org/0000-0001-6298-2087; Email: marc.petit@
sorbonne-universite.fr
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Authors
A. Sodreau − Sorbonne Universite, CNRS, Institut Parisien de
́
́
Chimie Moleculaire, UMR 8232, 75005 Paris, France
́
A. Vivien − Sorbonne Universite, CNRS, Institut Parisien de
́
Chimie Moleculaire, UMR 8232, 75005 Paris, France
́
A. Moisset − Sorbonne Universite, MONARIS, UMR 8233,
75005 Paris, France
́
C. Salzemann − Sorbonne Universite, MONARIS, UMR 8233,
75005 Paris, France
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c01641
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