Bimetallic Co/Al nanoparticles in an ionic liquid: Synthesis and application in alkyne hydrogenation

Article abstract of DOI:10.1039/c9nj03622a

Herein, we report the microwave-induced decomposition of various organometallic cobalt and aluminum precursors in an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm]NTf₂), resulting in Co/Al nanoalloys with different molar Co/Al ratios. The dual-source precursor system of dicobalt octacarbonyl (Co₂(CO)₈) and pentamethylcyclopentadienyl aluminum ([AlCp?]₄) in [BMIm]NTf₂ afforded CoAl nanoparticles (CoAl-NPs) with a molar Co/Al ratio of 1?:?1. Their size and size distribution were determined via transmission electron microscopy (TEM) to be an average diameter of 3.0 ± 0.5 nm. Furthermore, the dual-source precursor system of cobalt amidinate ([Co(ⁱPr₂-MeAMD)₂]) and aluminum amidinate [Me₂Al(ⁱPr₂-MeAMD)] in molar ratios of 1?:?1 and 3?:?1 resulted in CoAl-and Co₃Al-NPs with an average diameter of 3 ± 1 and 2.0 ± 0.2 nm, respectively. All the obtained materials were characterized via TEM, energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), together with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and (high-resolution) X-ray photoelectron spectroscopy ((HR-)XPS). Phase-pure Co/Al-NPs were not obtained since the concomitant formation of Co-NPs and Al₂O₃ occurred in this wet-chemical synthesis. The as-prepared Co/Al nanoalloys were evaluated as catalysts in the hydrogenation of phenylacetylene under mild conditions (2 bar H₂, 30 °C in THF). In comparison to the monometallic Co-NPs, the Co/Al-NPs showed a significantly higher catalytic hydrogenation activity. The Co-and Co/Al-NPs were also active under harsher reaction conditions (80 bar H₂, 80 °C) without the addition of the activating co-catalyst DIBAL-H.

Full text of DOI:10.1039/c9nj03622a

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Bimetallic Co/Al nanoparticles in an ionic liquid:
synthesis and application in alkyne
hydrogenation†
Cite this: New J. Chem., 2019,
43, 16583
a
b
a
a
Laura Schmolke,
Juri Barthel,
Bernhard J. Gregori, Beatriz Giesen, Alexa Schmitz,
c
d
d
b
Lena Staiger, Roland A. Fischer,
and Christoph Janiak
Axel Jacobi von Wangelin
*
a
*
Herein, we report the microwave-induced decomposition of various organometallic cobalt and aluminum
precursors in an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm]NTf ),
resulting in Co/Al nanoalloys with different molar Co/Al ratios. The dual-source precursor system of dicobalt
octacarbonyl (Co (CO) ) and pentamethylcyclopentadienyl aluminum ([AlCp*] ) in [BMIm]NTf afforded CoAl
2
2
8
4
2
nanoparticles (CoAl-NPs) with a molar Co/Al ratio of 1 : 1. Their size and size distribution were determined
via transmission electron microscopy (TEM) to be an average diameter of 3.0 Æ 0.5 nm. Furthermore,
i
the dual-source precursor system of cobalt amidinate ([Co( Pr
2
-MeAMD)
2
]) and aluminum amidinate
i
[
Me
2
Al( Pr
2
-MeAMD)] in molar ratios of 1 : 1 and 3 : 1 resulted in CoAl- and Co
3
Al-NPs with an average
diameter of 3 Æ 1 and 2.0 Æ 0.2 nm, respectively. All the obtained materials were characterized via TEM,
energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), together with high-
angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and (high-resolution)
X-ray photoelectron spectroscopy ((HR-)XPS). Phase-pure Co/Al-NPs were not obtained since the
Received 12th July 2019,
Accepted 23rd September 2019
concomitant formation of Co-NPs and Al
Co/Al nanoalloys were evaluated as catalysts in the hydrogenation of phenylacetylene under mild conditions
2 bar H , 30 1C in THF). In comparison to the monometallic Co-NPs, the Co/Al-NPs showed a significantly
higher catalytic hydrogenation activity. The Co- and Co/Al-NPs were also active under harsher reaction
conditions (80 bar H , 80 1C) without the addition of the activating co-catalyst DIBAL-H.
2 3
O occurred in this wet-chemical synthesis. The as-prepared
(
2
DOI: 10.1039/c9nj03622a
rsc.li/njc
2
8
as the synthesis of vitamin A. The vast majority of bimetallic
catalysts studied in the past decades are combinations of
Introduction
Nanoalloys are a promising class of catalysts due to their modular transition metals, typically involving noble metals with non-
9
10
composition of metallic components and surface characteristics, noble transition or main-group metals (e.g. Pd/Ga, Rh/Co,
1
–4
11
12
20
shapes, and sizes. One of the first applied bimetallic catalysts Cu/Co,
Pt/Co,
and Ru/Co ). Non-noble catalysts (e.g.
5
13
14
15
was the Lindlar catalyst for the semi-hydrogenation of alkynes.
4
Ni/Ga, Cu/Zn, and Fe Al13 ) have attracted considerable
The Lindlar catalyst consists of 4–6% Pd on calcium carbonate interest as low-cost alternatives to noble metal catalysts. The
6
,7
with lead acetate as a poison to prevent full hydrogenation.
second metal in nanoalloys is generally regarded as a promoter,
The catalyst is still important for industrial processes such which modulates the activity and/or selectivity of the catalyti-
1
6
cally active metal sites. Promotors can increase the turnover
a
17
Institut f u¨ r Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universit a¨ t
D u¨ sseldorf, D-40225 D u¨ sseldorf, Germany. E-mail: janiak@uni-duesseldorf.de;
Fax: +49-211-81-12287; Tel: +49-211-81-12286
frequency (NiPd/C ), modify the selectivity of a certain catalytic
5
reaction (Lindlar catalyst ) and improve the catalyst stability
1
8 23
b
c
(Co/Pt-NPs ). For example, the alloying of Pt nanocatalysts
with Sn enables the selective hydrogenation of cinnamic aldehyde
Institut f u¨ r Anorganische und Angewandte Chemie, Universit a¨ t Hamburg,
2
0146 Hamburg, Germany. E-mail: axel.jacobi@chemie.uni-hamburg.de
19
Ernst Ruska-Centrum f u¨ r Mikroskopie und Spektroskopie mit Elektronen (ER-C 2),
Forschungszentrum J u¨ lich GmbH, D-52425 J u¨ lich, Germany
Department of Chemistry, Technische Universit a¨ t M u¨ nchen, D-85748 Garching,
Germany
to a,b-unsaturated cinnamic alcohol. Bimetallic transition metal
2
0
20
21
Co/M-nanoparticle systems (Co/M = Co/Mn, Co/Re, Co/Ni,
d
21
Co/Fe and the previously noted noble-metal/cobalt-nanoalloys)
are well known as catalysts for the Fischer–Tropsch process.
Nanoalloys of non-noble transition metals with the electro-
†
Electronic supplementary information (ESI) available: IL and precursor analysis
TEM images with particle size histograms, SAEDs, EDX and XPS analysis, details
of the hydrogenation reactions. See DOI: 10.1039/c9nj03622a
2
2–24
positive main-group metals Al or Ga are far less explored.
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For example, Cokoja et al. reported the synthesis of CoAl, NiAl,
NJC
25
26
27
28
x 2
CuAl (x = 1 and 2) and CuE (E = Al and Ga) nanoparticles
via the wet-chemical hydrogenolysis of all-hydrocarbon precursors
in organic solvents. Sch u¨ tte et al. prepared NiGa-, Ni Ga - and
2
3
Ni Ga-NPs as noble metal-free catalysts for the semi-
3
1
3
hydrogenation of alkynes. The preparation of well-defined
Co/Al-nanoalloys has largely been under-utilized and their
catalytic properties are unknown. However, CoAl can be viewed
as a lighter and inexpensive homologue of the already reported
1
3
9
Ni/Ga and Pd/Ga nanoalloys.
The preparation of especially small (o5 nm) nanoalloys
bears great potential for catalytic application due to their high
dispersion in organic solvents and high surface-to-volume ratio
with a potentially high number of active sites. However, these
small nanoparticles may also undergo rapid agglomeration and
2
9,30
aggregation.
Thus, to prevent such deactivation, ionic
2
Scheme 1 Wet-chemical synthesis of Co/Al-NPs in [BMIm]NTf and their
liquids (ILs) have been employed as appropriate solvents and
stabilizing reagents in the synthesis and catalytic application of
application in alkyne hydrogenation reactions.
3
1–35
metal nanoparticles (M-NPs).
There is considerable interest in the application of bimetallic
organometallic precursors and Co/Al-NPs are hygroscopic and
air sensitive. Solvents were dried using an MBRAUN Solvent
Purification System and stored over molecular sieves. The final
water contents were checked by Karl Fischer titration, which
did not exceed 5 ppm. 1-Chlorobutane (499%) and 1-methyl-
imidazole (499%) were obtained from Sigma Aldrich and
purified by fractional distillation, then dried over 4 Å molecular
sieves for several days. Cobalt(II) chloride hexahydrate (98%)
was obtained from Sigma Aldrich and purified by recrystalliza-
3
6
nanomaterials in ionic liquids in catalysis. For example,
bimetallic Pd/Au-NPs in imidazolium ionic liquids showed
higher activity for hydrogenation reactions of different substrates
37
than monometallic Pd-NPs.
Electrostatic and steric interactions of ILs, which are other-
wise only weakly-coordinating, stabilize M-NPs with little
3
8–41
change in their surface properties.
Furthermore, the high
ionic charge, polarity and dielectric constant of ILs result in
excellent microwave absorption efficiencies, which enable
À3
tion in water and dried under high vacuum (10 mbar) at
4
2–44
effective heating by microwave irradiation.
Metal amidinates and metal carbonyls are well established as
organometallic) precursors in the soft and wet-chemical synthesis of
1
1
40 1C for serval days to obtain cobalt(II) chloride anhydrous.
,3-Diisopropylcarbodiimide (499%), methyllithium solution
(
(1.6 M in diethyl ether) and dicobalt octacarbonyl (490% Co,
45–51
M-NPs.
and their gaseous decomposition products are easily removed
They exhibit decomposition temperatures below 200 1C
moistened with hexane) were purchased from Sigma-Aldrich
and used without further purification. Lithium bis(trifluoro-
methanesulfonyl)imide (99%) was purchased from abcr and
used without further purification. The low valent cobalt(II)
5
2–57
so that product contamination is minimized.
Monometallic
58
Co-NPs have been applied in catalytic hydrogenation reactions of
various substrates such as nitriles, ketones and aldehydes,
and alkenes, albeit their activity is low in comparison
with e.g. Ni-NPs under similar conditions. Moreover, Fe-NPs are
59
60,61
bis(trimethylsilyl)amide ([Co(btsa) ]) was prepared according
2
62,63
64
alkynes
68
4
to a literature procedure. Furthermore, [(AlCp*) ] was prepared
65
69
according to the literature.
known photoactive catalysts for the hydrogenation of alkynes and
66
alkenes. Metallic Co/Al-NPs appear to be unknown in catalytic
hydrogenation reactions. Wang et al. reported CoAlO -NPs for the
Instrumentation
x
67
catalytic hydrogenation of CO to ethanol.
Coulometric Karl Fischer titration was performed with an ECH/
2
Herein, we investigate the possibilities to prepare Co/Al-NPs ANALYTIK JENA AQUA 40.00 Karl Fischer titrator. The measure-
via wet-chemical synthesis through the microwave-assisted ments were performed using the headspace module with a dry
thermal decomposition of various organometallic cobalt and sample container and crimp caps (+ = 20 mm, with PTFE
aluminum complexes in an ionic liquid. The aim of this study septum). The sample containers and crimp caps were dried at
is to derive a controllable synthesis route for Co/Al-NPs, which 70 1C for 2 days. The measurements were performed in an oven
are still difficult to obtain, and to examine their catalytic at a temperature of 170 1C.
properties in alkyne hydrogenation reactions (Scheme 1).
All ion chromatographic measurements (IC) were carried
out using a Dionex ICS 1100 instrument with suppressed
conductivity detection. The suppressor (AERS 500, Dionex)
was regenerated with an external water module. The system
was equipped with an analytical IonPac AS 22 column from
Experimental
Materials
All synthetic experiments were carried out under a nitrogen Dionex (4 Â 250 mm) with the corresponding guard column AG
or argon atmosphere using Schlenk techniques since the 22 (4 Â 50 mm). The instrument was controlled using the
1
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Paper
s
Chromeleon
software (version 7.1.0.898). The injection for the injection. Column: HP-5, 19091J-413 (30 m  320 mm Â
À1
volume was 25 mL. The standard eluent used was a 4.5 mmol L
Na CO + 1.0 mmol L NaHCO mixture with an addition of n-pentadecane.
0.25 mm), carrier gas: nitrogen and internal standard:
À1
2
3
3
30 vol% acetonitrile (ACN).
Gas chromatography with mass spectrometry detector
Thermogravimetric analysis (TGA) was carried out with a (GC-MS). An Agilent 6890 N Network GC-system with a mass detector
Netzsch TG 209 F3 Tarsus, equipped with an Al-crucible at a 5975 MS was used for GC-MS analysis. A split mode was used for the
À1
heating rate of 5 K min under an inert atmosphere (N
2
).
injection. Column: SGE-BPX5 (30 m  250 mm  0.25 mm) and
TEM imaging was performed on an FEI Tecnai G2 F20 carrier gas: hydrogen.
electron microscope operated at an accelerating voltage of
00 kV. Digital images were recorded using a Gatan UltraScan Ionic liquid synthesis
7
0
2
1000P detector. Samples were prepared using 200 mm carbon-
The ionic liquid [BMIm]NTf was synthesized by reacting 1-methyl-
2
coated copper grids or gold grids. The size distribution was
determined manually or with the aid of the Gatan DigitalMicro-
graph software by counting at least 100 individual particles.
TEM-EDX spectroscopy was also performed on the FEI
Tecnai G2 F20 with a high-angle energy dispersive X-ray detector
providing a resolution of 136 eV or better for Mn K-a radiation.
The exposure time of individual EDX spectra was 3 min.
Selected area electron diffraction (SAED) patterns were
recorded with an FEI Titan 80–300 TEM operated at an
accelerating voltage of 300 kV. The area selection was achieved
with a round aperture placed in the first intermediate image
plane with a corresponding diameter of 0.64 mm in the object
plane. For each acquisition, a sample region with a significant
amount of material was placed inside the aperture. The object
was illuminated with a wide-spread parallel beam to obtain
focused diffraction patterns. The diffraction images were
calibrated with Debye–Scherrer patterns recorded from a gold
reference sample (S106, Plano GmbH, Wetzlar, Germany).
High-angle annular dark-field scanning transmission electron
microscopy (HAADF-STEM) micrographs were taken at room
temperature with an FEI Tecnai G2 F20 TEM operated at an
accelerating voltage of 200 kV. Samples were deposited on 200 mm
carbon-coated gold or copper grids.
imidazole with 1-chlorobutane to yield [BMIm]Cl. [BMIm]Cl and
79
LiNTf
2
reacted to give [BMIm]NTf
2
.
Following washing with
À7
water, the IL was dried under ultra-high vacuum (10 mbar)
at 60 1C for one day. The characterization was carried out by
1
13
19
H-, C- and F-NMR. The IL purity was assessed by ion
s
chromatography (Dionex ICS-1100, with IonPac AS22, 4 Â
50 mm column) to be 499.9% (Fig. S1, ESI†). Its water content
by coulometric Karl Fischer titration was less than 10 ppm.
2
7
1
1
3
H-NMR (CDCl
.3 Hz, –CH , 3H), 1.36 (h,
q, JHH = 7.5 Hz, –CH , 2H), 3.93 (s, –CH
.5 Hz, –CH , 2H), 7.3 (q,
3 HH
, 300 MHz, 298 K): d/ppm = 0.95 (t, J =
3
7
(
7
3
J
HH = 7.3 Hz, –CH
, 3H), 4.16 (t, JHH
HH = 2.0 Hz, 2x-CH, 2H), 8.72
, 75 MHz, 298 K): d/ppm = 13.32
–C), 32.04 (s, C–CH –C), 36.45
s, N–CH ), 50.08 (s, N–CH –C), 119.92 (q, CF ), 122.37
2
, 2H), 1.84
3
3
2
3
=
3
2
J
13
(
(
(
(
(
s, –CH
s, C–CH
3
, 1H). C-NMR (CDCl
), 19.45 (s, C–CH
3
3
2
2
3
2
3
19
s, CHQC) 123.80 (s, CHQC), 136.19 (s, N–CH–N). F-NMR
without solvent, 41 MHz, 298 K) d/ppm = À78.4.
Metal precursor synthesis
Lithium amidinate was synthesized via the deprotonation and
methylation of 1,3-diisopropylcarbodiimide with methyllithium
À1
(
1.6 mol L in diethyl ether). The resulting lithium amidinate
was reacted in a salt metathesis reaction with the purified
cobalt(II) chloride anhydrous according to the literature
X-ray photoelectron spectroscopy, XPS-(ESCA-) measure-
ments were performed with a Fisons/VG Scientific ESCALAB
5
4,72 1
(Scheme 2).
6 6
H-NMR (C D , 500.13 MHz, 297 K): d/ppm =
2
7
00X xp-spectrometer, operating at 70–80 1C, a pressure of
À9
À69 (br, 24H), 301 (br, 6H), 320 (br, 4H).
.0 Â 10
mbar and sample angle of 331. Spectra were
excitation (11 kV, 20 mA)
Aluminum amidinate was synthesized via the reaction of
recorded using polychromatic Al-K
a
1
,3-diisopropylcarbodiimide with trimethylaluminum (2.0 M
at an emission angle of 01 and were referenced to the carbon 1s
orbital with a binding energy of 284.8 eV. Calibration of the XPS
7
3 1
in hexane) according to the literature (Scheme 3).
H-NMR
3
(CDCl , 300 MHz, 297 K) d/ppm = 3.48 (sept, 2H, J = 6.3 Hz),
was carried out by recording spectra with Al-K
a
X-rays from
3
HH
3
13
1.85 (s, 3H), 0.97 (d, 12H, J = 6.1 Hz), –0.88 (s, 6H). C-NMR:
clean samples of copper, silver and gold at 50 eV and 10 eV pass
energies and comparison with reference values. Fitting of the
experimental XP spectra was done with the CasaXPS program,
version 2.3.19PR1.0, Copyright 1999–2018 Casa Software Ltd.
Short contact with air during sample transfer to the XPS
instrument could not be avoided and may have led to surface
oxidation.
HH
(
(
CDCl
s, CHMe
Co(btsa)
3
, 75 MHz, 297 K) d/ppm = 171.16 (s, CMe), 44.42
), 24.63 (s, CHMe ).
), 10.35 (s, CMe), À10.65 (br, AlMe
] (0.301 g, 0.8 mmol) and [AlCp*] (0.129 g,
2
2
2
[
2
4
0
8
.8 mmol) were suspended in 10 mL toluene and heated to
0 1C for 3 h. All volatiles were removed under reduced pressure.
Autoclaves for hydrogenation reactions. A high-pressure
s
reactor (Parr ), which was loaded in a glovebox, was used for
hydrogenation reactions. Hydrogen gas was purchased from
Praxair (99.9992%).
Gas chromatography with flame ionization detector (GC-FID).
A HP6890 GC-system with an injector 7683B and an Agilent 7820A
i
Scheme 2 Synthetic scheme for [Co( Pr
2
-MeAMD)
2
]
from 1,3-diiso-
system was used for GC-FID analysis. A split-less mode was used propylcarbodiimide, methyllithium and cobalt(II) chloride.
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a glove box. The mixture was stirred for 18 h at room tempera-
ture and the resulting dark dispersion was decomposed in a
microwave (CEM, Discover) for 30 min at 230 1C (50 W). The
dispersion became black, and was then washed with aceto-
nitrile (3 Â 2 mL) and centrifuged. The resulting material was
dried under high vacuum until a black powder was obtained.
i
Scheme 3 Synthetic scheme for [Me
2
Al( Pr
2
-MeAMD)] from 1,3-diiso-
propylcarbodiimide and trimethylaluminum.
Preparation of CoAl/Co
3
Al-NPs (NP4). Samples of 61 mg
-MeAMD) ] and 26 mg (0.131 mmol)
-MeAMD)] were combined in a microwave vessel in
.35 g [BMIm]NTf (to yield 1 wt% Co/Al in the IL dispersion) in
i
(
[
1
0.178 mmol) [Co( Pr
Me Al( Pr
2 2
2
2
i
2
a glove box. The mixture was stirred for 16 h at room tempera-
ture and the resulting dark dispersion was decomposed in a
microwave (CEM, Discover) for 30 min at 230 1C (50 W). The
dispersion became black, and was then washed with aceto-
nitrile (3 Â 2 mL) and centrifuged. The resulting material was
dried under high vacuum until a black powder was obtained.
2
Scheme 4 Synthetic scheme for [Cp*Co(m-H)(Al(k -(CH
Me )(btsa))] from [Co(btsa) ] and [AlCp*] .
3 2 4
2
SiMe
2
)NSi-
7
4 1
The product was recrystallized in n-hexane (Scheme 4). H-NMR
Preparation of Co-NPs (NP5). Samples of 27 mg (0.077 mmol)
i
(
C
6
D
6
, 300 MHz rt): d/ppm = 81.03 (br, s, Cp*), 1.21 (s, btsa), 0.49 [Co( Pr -MeAMD) ] and 14 mg (0.087 mmol) [(AlCp*) ] were
2
2
4
13
(s, btsa), À0.58 (s, btsa). C-NMR (C
6
D
6
, 75 MHz rt): d/ppm = combined in a microwave vessel in 1.37 g [BMIm]NTf (to yield
2
9
.60–4.34 (overlapping multiplets, btsa).
0.5 wt% Co/Al in the IL dispersion) in a glove box. The mixture
was stirred overnight at room temperature and the resulting
dark dispersion was decomposed in a microwave (CEM, Discover)
Metal nanoparticle (M-NP) synthesis
Decomposition by microwave heating was carried out under for 30 min at 230 1C (50 W). The dispersion became black, and
an argon atmosphere. The masses of the organometallic was then washed with acetonitrile (3 Â 2 mL) and centrifuged.
precursors were set to yield 0.5 or 1.0 wt% Co/Al-NPs in the The resulting material was dried under high vacuum until a black
IL dispersion. The parameters for the microwave-induced M-NP powder was obtained.
1
3,34,45–48,75
synthesis were modified from the literature procedures.
Preparation of Co-NPs (NP6). 9 mg (0.029 mmol) [Cp*Co(m-H)-
2
All analyses (TEM, STEM, EDX, SAED and XPS) were performed (Al(k -(CH SiMe )NSiMe )(btsa))] were suspended in a microwave
2
2
3
with purified M-NPs. At the chosen temperature of 230 1C, no IL vessel in 0.49 g [BMIm]NTf (to yield 0.5 wt% Co/Al in the IL
2
1
19
decomposition was seen by TGA, H- and F-NMR even by holding dispersion) in a glove box. The mixture was stirred overnight
this temperature for 8 h (Fig. S3, ESI†). at room temperature and the resulting dark dispersion was
Preparation of CoAl-NPs (NP1). In a microwave vessel, 9 mg decomposed in a microwave (CEM, Discover) for 30 min at
0.055 mmol) [(AlCp*) ] and 10 mg (0.058 mmol) Co (CO) were 230 1C (50 W). The dispersion became black, and was then
dispersed in 1.00 g [BMIm]NTf
(to yield 1 wt% Co/Al in the IL washed with acetonitrile (3 Â 2 mL) and centrifuged. The
dispersion) in a glove box. The yellow dispersion was heated to resulting material was dried under high vacuum until a black
5 1C for 5 h and became dark red. After cooling to room powder was obtained.
temperature, the red dispersion was stirred overnight and then Preparation of Co-NPs (NP7). 236 mg (0.690 mmol)
decomposed in a microwave (CEM, Discover) for 30 min at [Co( Pr
30 1C (50 W). The dispersion became black, and was then were suspended in a microwave vessel in 2.01 g [BMIm]NTf
(
4
2
8
2
6
i
2
-MeAMD)
2
] (to yield 1 wt% Co in the IL dispersion)
in
2
2
washed with acetonitrile (3 Â 2 mL) and centrifuged. The a glove box. The mixture was stirred overnight at room tem-
resulting material was dried under high vacuum until a black perature and the resulting dark dispersion was decomposed in
powder was obtained.
a microwave (CEM, Discover) for 30 min at 230 1C (50 W). The
Preparation of CoAl-NPs (NP2). Samples of 56 mg dispersion became black, and was then washed with aceto-
i
(
[
0.163 mmol) [Co( Pr -MeAMD) ] and 32 mg (0.163 mmol) nitrile (3 Â 2 mL) and centrifuged. The resulting material was
2
2
i
Me Al( Pr -MeAMD)] were combined in a microwave vessel in dried under high vacuum until a black powder was obtained.
2 2
1
2
.45 g [BMIm]NTf (to yield 1 wt% Co/Al in the IL dispersion) in
General procedure for the catalytic hydrogenations with
Co]-NPs
a glove box. The mixture was stirred for 18 h at room tempera-
ture and the resulting black dispersion was decomposed in a
[
microwave (CEM, Discover) for 30 min at 230 1C (50 W). The Under an atmosphere of argon (Schlenk technique or glove
dispersion became black, and was then washed with aceto- box), an oven-dried 4 mL vial with a stirring bar was charged
nitrile (3 Â 2 mL) and centrifuged. The resulting material was with alkyne (0.2 mmol) and n-pentadecane as an internal
dried under high vacuum until a black powder was obtained.
GC reference (0.2 mmol, 42.5 mg). The catalyst (5–10 mol%
Preparation of Co Al-NPs (NP3). Samples of 71 mg [Co]-NPs, 10–20 mol% DIBAL-H) and 0.4 mL THF were added
3
i
(
0.208 mmol) [Co( Pr
2
-MeAMD)
-MeAMD)] were combined in a microwave vessel in punctured with a short needle and the vial was transferred to
.42 g [BMIm]NTf (to yield 1 wt% Co/Al in the IL dispersion) in a pressure-resistant reactor equipped with a gas inlet. The reactor
2
] and 13 mg (0.066 mmol) and the vial was closed with a septum. The septum was
i
2 2
[Me Al( Pr
1
2
1
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was purged with H
Paper
2
for 1 min while stirring the reaction mixture. composition. Each sample was analyzed on a large scale and
2
After three short cycles of purging with H by pressurizing and TEM images were taken from different positions on the grid to
depressurizing (2.0 bar, 5 s, 1.3 bar), the H2 pressure and ensure the representative nature of the chosen particle ensemble.
temperature were set (2 bar H , 30 1C). After 5–16 h, the reactor Small Co/Al-NPs with an average size between 2 nm (NP3) and
2
was cooled, and the pressure released. The vials were retrieved, 5 nm (NP4) and small size dispersions of Æ 0.2–1 nm were readily
3
and saturated aqueous NaHCO (1.5 mL) and ethyl acetate obtained, according to the TEM analysis (Table 1).
i
(
1.5 mL) were added to extract the metal catalyst into the aqueous
phase for protection of the GC. The resulting suspension was [BMIm]NTf
stirred for 20 min, after which the organic phase was separated average size of 10 Æ 3 nm, besides ill-defined amorphous Al
and filtered through a short SiO plug. Yields were determined (Fig. S21–S23, ESI†). The formation of Al-fluorides or oxyfluorides
The decomposition of [Co( Pr
2 2 4
-MeAMD) ] and [(AlCp*) ] in
2
(NP5) resulted in monometallic Co-NPs with an
2
from quantitative GC and NMR analyses vs. internal references.
was ruled out by XPS (see below). Also for the synthesized single-
2
source precursor [Cp*Co(m-H)(Al(k -(CH SiMe )NSiMe )(btsa))] in
2
2
3
[
BMIm]NTf (NP6) only monometallic Co-NPs with average size of
2
Results and discussion
26 Æ 6 nm could be observed (Table S4 and Fig. S24–S26, ESI†).
i
Pure Co-NPs (NP7) were synthesized from [Co( Pr
2 2
-MeAMD) ] in
i
The metal precursors Co
2
(CO)
-MeAMD)] or [Co( Pr
were suspended in the dried [BMIm]NTf
4 h under an argon atmosphere to achieve a fine dispersion.
8
and [(AlCp*)
4
], [Co( Pr
2
-MeAMD)
2
]
2
[BMIm]NTf for the investigation of the influence of aluminum on
i
i
and [Me
2
Al( Pr
2
2
-MeAMD)
2
] and [(AlCp*)
IL for at least
4
]
the catalytic activity of the Co/Al-NPs (NP2 and NP3). Further
information is given in the ESI† (Fig. S12–S17).
2
2
2
Furthermore, the single-source precursor [Cp*Co(m-H)(Al(k - Thermal decomposition of Co
CH SiMe )NSiMe )(btsa))] with a specific metal ratio and a
2 8 4
(CO) and [(AlCp*) ]
(
2
2
3
For the synthesis of the CoAl-NPs (NP1), small NPs with an
average size of 3.0 Æ 0.5 nm were obtained. Most of the NPs
were immobilized on an amorphous background (Fig. 1). The
only crystalline phase in the NPs was identified by SAED to be
face-centered cubic (fcc) CoAl (Fig. S9, ESI†). The SAED patterns
were measured at different positions on the TEM grid to ensure
the crystalline phase identity within the sample. EDX mapping
in STEM indicated the presence of aluminum in the back-
ground and also in the areas around the NPs, whereas cobalt
was only localized in the large NPs (orange window in Fig. 1).
CoAl-NPs of 3 nm are not clearly visible in the EDX map (map
size B50 nm). The map shows obviously 20 nm large Co
particles. The sampling of the map is too coarse to clearly
image small NPs. Thus, the small CoAl-NPs appear as a diffuse
background surrounding the large Co particles. Furthermore,
EDX spectra were measured in TEM mode to determine the
element composition over a larger segment (Fig. S10, ESI†).
The TEM-EDX analysis suggests a significant compositional
variation of Co : Al molar ratios ranging between 1 : 1 and 1 : 2
2
Co–Al bond was suspended in [BMIm]NTf overnight. The NP
synthesis in IL was achieved by microwave irradiation using a
power of 50 W to give an approximate temperature of 230 1C
in the reaction mixture for 30 min (Scheme 5). A black NP
dispersion was reproducibly obtained by decomposition of the
organometallic precursors in the IL. Thermogravimetric analysis
(
TGA) revealed the full decomposition of the organometallic
precursors at temperatures between 83 1C and 95 1C (Table S1
and Fig. S6, ESI†), whereas the [BMIm]NTf IL decomposes at a
2
temperature higher 424 1C (Fig. S2, ESI†). Based on the TGA
measurements, a temperature of 230 1C was selected for all
microwave-assisted thermal NP syntheses to achieve complete
decomposition of the precursors and keep the formation of
by-products as low as possible. At 230 1C, no IL decomposition
1
19
was seen by TGA, H- and
F-NMR, even by holding the
temperature for 8 h (Fig. S3–S5, ESI†).
The morphology, crystalline phase, size and size dispersion
of the purified Co/Al-nanoalloys were analyzed by TEM and
SAED, together with HAADF-STEM and (HR-)XPS. The charac-
terization was completed by EDX (in combination with TEM or
EDX mapping with STEM) to determine the qualitative metal
(
Æ10 at% rel. error) at four different places on the TEM grid.
Additionally, the signals of oxygen and sulfur in all the EDX
spectra indicate the presence of residual IL. XPS analysis of NP1
was carried out for further element composition investigations
(
Fig. 2 and Table 2). The survey spectrum identified aluminum,
carbon, nitrogen, oxygen, fluorine, and cobalt (Fig. S11, ESI†).
Nitrogen and fluorine indicate the presence of residual [BMIm]NTf
2
on the nanoparticle surface. HR-XPS were measured from
aluminum, oxygen, fluorine and cobalt. The HR-XP spectra of
the F 1s peak identified, as assumed before, organic fluorine
from the IL at 690 eV but also small amounts of inorganic
fluoride, presumably cobalt fluoride at 686 eV (Table 2 and
7
6
Fig. 2). Thus, the IL can also take part in the metal precursor
decomposition by serving as a fluoride source. According to ion
chromatography (IC), the IL contains only a very small amount
of fluoride ions (o1 ppm). Hence, only the bis(trifluoromethyl-
Scheme 5 Synthesis of Co/Al-NPs from Co
2
(CO)
-MeAMD)] in different molar ratios
NP2 and NP3) by microwave (MW)-assisted thermal decomposition in
BMIm]NTf
8 4
and [(AlCp*) ] (NP1) or
i
i
2 2 2 2
from [Co( Pr -MeAMD) ] and [Me Al( Pr
(
[
7
7,78
2
.
sulfonyl)imide (triflimide) anion can be the fluoride source.
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a
Table 1 M-NP size determination for Co/Al-NPs
b
c
d,e
Batch
Precursor
Co (CO) [(AlCp*)
Co : Al
Crystalline phase
TEM + [nm]
NP1
NP2
NP3
NP4
NP5
NP6
NP7
2
8
4
]
1 : 1
1 : 1
3 : 1
1.5 : 1
1 : 1
—
CoAl
CoAl
3.0 Æ 0.5
3 Æ 1
i
i
[Co( Pr
2
2
2
2
-MeAMD)
-MeAMD)
-MeAMD)
-MeAMD)2
2
] [Me
] [Me
] [Me
2
2
2
Al( Pr
2
2
2
-MeAMD)]
-MeAMD)]
-MeAMD)]
i
i
[Co( Pr
2
2
Al( Pr
Co
CoAl/Co
3
Al
2.0 Æ 0.2
5 Æ 1
i
i
[Co( Pr
Al( Pr
3
Al
i
[Co( Pr
2
] [(AlCp*)
4
]
Co
Co
Co
10 Æ 3
26 Æ 6
3 Æ 1
[Cp*Co(m-H)(Al(k -(CH
2
SiMe
2
)NSiMe
3
)(btsa))]
i
[Co( Pr
2
-MeAMD)
2
]
—
a
b
0
.5/1.0 wt% M-NP/IL dispersions obtained by microwave-assisted heating for 30 min at 230 1C. Applied molar ratio of precursors in dual-source
c
precursor systems. The crystalline phase of the NPs was determined by SAED. Non-crystalline phases are not identified by this technique.
d
e
Average diameter (+). See Experimental section for TEM measurement conditions; at least 100 particles were used for the size analysis.
Table
2
Comparison of XPS binding energies in sample NP1 in
a
[
BMIm]NTf
2
77,80–84
XPS signal NP1 deconvoluted bands Characteristic regions
0
Co 2p3/2 [eV] 778.5 (23%)
Co 778.1–783.1
CoO 780.0–786.0
781.1–788.0 (77%)
3 4
Co O 779.6–789.5
CoF2 780.9
ÀI
0
F 1s [eV]
O 1s [eV]
686.0 (57%)
689.6 (43%)
F
684–685.5
Fig. 1 TEM image (left), HAADF-STEM image (middle) and EDX-mapping
F 688–689
(
right) of cobalt (blue) and aluminum (yellow) in NP1 obtained by thermal
ÀII
ÀII
531.8 (44%)
O
O
529–530
+II/+III
decomposition of Co (CO) and [(AlCp*) ] in [BMIm]NTf . The orange
2
8
4
2
532.9 (56%)
in Co
-oxide 530–532.9
window in the HAADF-STEM image displays the area of EDX mapping.
The yellow window displays the reference window, to see possible move-
ment of the sample during the EDX mapping. See Fig. S8, ESI† for further
TEM images and histogram of the particle size distribution.
0
O 531.5–533
0
Al 2p [eV]
73.6 (6%)
4.9 (94%)
Al 72.7
7
Al
AlOF
AlF
2
O
3
74.1
75.9
x
3
78.1
a
XPS was performed with purified M-NPs. The NP-IL dispersion was
washed several times with 2 mL acetonitrile each to remove the IL. The
resulting material was dried under high vacuum until a black powder
could be obtained.
possible passivation by aluminum. The quantification of cobalt
and aluminum over the entire sample gave a Co : Al molar ratio
of 1 : 1.
Altogether the sample NP1 shows the presence of crystalline
2 3
CoAl-NPs on an amorphous alumina (Al O ) background
Fig. 2 HR-XPS of sample NP1 (0.5 wt% CoAl-NPs in [BMIm]NTf
2
from together with amorphous Co-oxide nanoparticles, the XPS-
Co (CO) and [(AlCp*) ]). HR-spectra of Al 2p, O 1s, F 1s and Co 2p3/2
2
8
4
.
elucidated formation of alumina and Co-oxide is most likely
due to the oxidation of metal species, as described in the
25,82
literature and will be discussed later using the XPS results.
Thus, we interpreted the reaction product as a mixture of CoAl, Co
and Al nanoparticles, with the latter being easily and rapidly
oxidized. The synthesis of phase-pure Co/Al-NPs, that is, without
the simultaneous formation of Co-NPs and Al O , may be difficult
2 3
to achieve by this wet-chemical synthetic route.
The analysis of the IL by NMR after the NP synthesis, with only
traces of metal fluoride formed, gave no indication of its
decomposition because of the trace amounts. The O 1s orbital
indicates two different oxygen species (Table 2 and Fig. 2). The
7
6
2 3
first species at 532 eV can ascribed to Al O and the second
7
9
species at 533 eV to organic C–O. The oxidation of the
aluminum can be confirmed by the Al 2p orbital. The binding
i
Thermal decomposition of [Co( Pr
2
2
-MeAMD) ] and
i
III
80
[Me Al( Pr -MeAMD)]
2
2
energy at 75 eV indicates an Al species. AlF3 would be
8
1
i
located at higher binding energies around 78 eV. Whereas The thermal decomposition of [Co( Pr -MeAMD) ] and
2
2
8
1
i
Al
with air during sample transfer to the XPS instrument could at 230 1C using a power of 50 W for 30 min led to the formation
not be avoided and may have led to surface oxidation. The of small CoAl-NPs (NP2) and Co Al-NPs (NP3) with an average
oxidation of Co and Al will be discussed later with regard to size of 2.0 Æ 0.2 nm and 3 Æ 1 nm. As can be seen for the
2 3 3
2 2 2
O and Al(OH) are localized at around 74 eV. Short contact [Me Al( Pr -MeAMD)] in various molar ratios in [BMIm]NTf
3
1
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Table 3 Comparison of the XPS binding energies in samples NP2 and NP3
a
2
in [BMIm]NTf
XPS
signal
NP2 deconvoluted NP3 deconvoluted Characteristic
77,80–82,84
bands
bands
regions
0
Co 2p3/2 778.0 (13%)
779.4 (9%)
Co 778.1–783.1
7
80.7–787.2 (87%) 780.9–787.3 (91%) CoO 780.0–786.0
3 4
Co O 779.6–789.5
ÀI
0
F 1s
O 1s
685.1 (86%)
—
F
684–685.5
688.2 (14%)
F 688–689
ÀII
531.1 (100%)
530.0 (45%)
O
529–530
Fig. 3 HR-TEM images and SAEDs of fcc CoAl (NP2) and fcc Co
3
Al (NP3)
(CoAl
+II/+III
531.6 (55%)
Co
530–532.9
i
i
85
0
from [Co( Pr
left) and Co
2
-MeAMD)
2
] and [Me
2
Al( Pr
2
-MeAMD)] in [BMIm]NTf
2
O 531.5–533
86
(
3
Al (right) reference reflexes in red, face-centered cubic (fcc)
0
structures with space groups Pm 3% m).
Al 2p
73.3 (16%)
71.2 (6%)
Al 72.7
73.9 (84%)
73.0 (94%)
Al
AlF
2
O
3
3
74.1
78.1
sample of NP4, the molar ratios of the precursors must be
a
XPS was performed with purified M-NPs. The NP-IL dispersion was
exactly 1 : 1 or 3 : 1 for the synthesis of CoAl- or Co
Co : Al precursor ratio of 1.5 : 1, a mixture of CoAl and Co Al-NPs
3
3
Al-NPs. At a washed several times with 2 mL acetonitrile each to remove the IL. The
resulting material was dried under high vacuum until a black powder
was obtained.
was obtained (Table 1 and Fig. S18–S20, ESI†).
A high degree of agglomeration was observed for both
composites. Furthermore, impurities as an amorphous back-
ground could be observed. The SAED patterns indicate the
formation of crystalline fcc CoAl for NP2 and fcc Co
3
Al for
NP3. We noted that Co Al as nanoparticles was hitherto
3
unknown. The SAED patterns were measured at different posi-
tions on the TEM grid to ensure crystalline phase identity
within the sample.
The element compositions were determined by EDX
(
in combination with TEM) at three different positions. The
TEM-EDX analysis suggests an excess of aluminum for NP2
1 : 2, 2 : 3, and 1 : 3). This aluminum excess is derived from the
(
i
Fig. 4 HR-XPS of sample NP2 (1.0 wt% CoAl-NPs from [Co(Pr
2
-MeAMD)
2
]
presence of aluminum in the amorphous background, as
described for NP1. For NP3 the TEM-EDX spectra indicate an
excess of cobalt (5 : 1, 5 : 1, and 3 : 1) and indicate that cobalt is
present in the amorphous impurities. In both samples NP2 and
NP3, impurities of sulfur, carbon and oxygen from the IL were
identifiable. It was not possible to identify the amorphous
background. The TEM-EDX image only indicates the presence
i
2 2 2
and [Me Al( Pr -MeAMD)] in [BMIm]NTf ). HR-spectra of Al 2p, Co 2p3/2,
F 1s and O 1s.
x y
of aluminum in the background. Thus, different Co Al or Al
phases are conceivable. However, it was not possible to synthe-
size Co/Al-NPs without this background irrespective of which
precursors were used (Table 1). Again, it is evident that the
synthesis of phase-pure Co/Al-NPs via a wet-chemical synthetic
route remains a challenge.
XPS analysis was used to verify the element compositions of
the samples (Table 3 and Fig. 4, 5). Both samples showed the
partial oxidation of cobalt (13% Co for NP2 and 9% Co for
i
Fig. 5 HR-XPS of sample NP3 (1.0 wt% Co
3
Al-NPs from [Co(Pr
2 2
-MeAMD) ]
0
0
i
2 2 2
and [Me Al( Pr -MeAMD)] in [BMIm]NTf ). HR-spectra of Al 2p, Co 2p3/2
NP3) and aluminum caused by their contact with air during the and O 1s.
sample preparation. The quantification of cobalt and alumi-
num over the entire sample gave a Co : Al molar ratio of 1 : 1 for
NP2 and 3 : 1 for NP3. HR-XPS of Al 2p indicates the oxidation
The binding energy for the Co 2p orbital of around 779 eV
3
/2
0
III
0
+II
+III
of Al to Al . Particularly Al O is a possibility, while the is indicative of a Co species. Co /Co
species occur at
can be excluded (Table 3 and binding energies of 780–782 eV. A differentiation between
Fig. 4, 5). The XPS results indicate a correlation between the CoO and Co is not possible because there is no significant
oxidation state of cobalt and the molar ratio of cobalt to difference in the binding energies between CoO, Co(OH)
2
3
3 x
presence of AlF and AlOF
3 4
O
2
,
8
7
0
aluminum in the NPs (Fig. 6).
Co
3
O
4
and CoAl
2
O
4
of Co 2p3/2
.
The relative amount of Co
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Hydrogenation reaction with Co-, CoAl- and Co
3
Al-NPs
Cobalt-based catalysts are well known in catalytic hydrogenation
6
3–65
reactions.
Several reactions can be catalyzed, such as the
59,89–92
59,91–95
59,92,93,96–98
hydrogenation of CQO,
CQN,
and CQC.
For example, Beller and co-workers reported N-graphitic-
modified Co-NPs for the selective semi-hydrogenation of alkynes
6
4
(
1 mol% Co-catalyst, 30 bar H , 120 1C in acetonitrile). Herein,
2
we applied the prepared Co- and Co/Al-NP samples NP7 (Co),
NP2 (CoAl), and NP3 (Co Al) for the hydrogenation of alkenes
3
and alkynes. NP7 in IL showed low catalytic activity in the
hydrogenation of the model substrate phenylacetylene
(
Table 4 and Fig. S5, S7, ESI†). Therefore, the NPs were applied
under IL-free conditions by washing the freshly prepared
NP@IL several times with acetonitrile to remove [BMIm]NTf
2
,
Fig. 6 Comparison of the HR-spectra of Co 2p3/2 of NP1 (blue), NP2 (red),
NP3 (green) and NP7 (black) in the range of 776 eV to 794 eV.
followed by high-vacuum solvent evaporation. However, even
with extensive washing it was difficult to remove the directly
adhering IL (monolayer) on the NP surface. The signals in the
seems to decrease when going from CoAl species (in samples EDX spectra for sulfur and fluorine and in the XPS for CF
NP1 and NP2) over Co
Al (sample NP3) to neat Co (sample confirm residual IL. The SAED patterns indicate the formation
NP7). The latter has almost no signal intensity at around of crystalline fcc CoAl for NP2 and fcc Co Al for NP3 (Fig. 3).
79 eV. It is evident that samples NP1 to NP3 show a significant Powder X-ray diffraction yielded no diffractograms probably
oxidation of cobalt caused by the unavoidable contact with air due to the small nanoparticle sizes. The aluminum-free
3
3
3
7
8
8
during the sample preparation for XPS.
The striking difference is the full oxidation of what should (80 bar H
have been pure Co-NPs in sample NP7. This suggests a protection Co Al-NPs under these same conditions gave complete con-
Co-NPs (NP7) were inactive even under harsh conditions
, 80 1C, Table 4, entry 2), whereas the CoAl- and
2
3
or oxygen scavenger effect of the easier to oxidize aluminum versions, albeit with low chemoselectivities (Table 4, entries 5
content in samples NP1 to NP3 upon the short air contact during and 10, respectively). To apply milder reaction conditions,
25
sample transfer to the XP spectrometer. Further, comparing the diisobutylaluminium hydride (DIBAL-H) was used as a co-catalyst
‘CoAl’’ samples NP1 and NP2 with the ‘‘Co Al’’ sample NP3, there to enhance the catalytic activity of the Co-NPs, most likely as a
‘
3
0
is also a larger relative Co proportion in the former. This consequence of cobalt oxide reduction to cobalt(0) on the surface of
supports the aluminum scavenger effect since samples NP1 and the nanoparticles.
59,91,95,99–102
NP2 also contain an equimolar amount of aluminum, whereas
NP3 has only one Al for three Co equivalents.
DIBAL-H itself, showed no significant catalytic activity under
the same conditions (Table 4, entry 15).
3
Table 4 Catalyst screening of NP7 (Co), NP2 (CoAl), NP3 (Co Al) and NP7-IL (Co-NP in IL)
a
Entry
Catalyst
Additive
T [h]
Conditions
Conversion [%]
Styrene [%]
Ethyl benzene [%]
1
2
3
4
5
6
7
8
9
10 mol% NP7
—
—
24
24
24
24
24
24
24
6
24
24
24
24
6
A
B
A
A
B
A
C
C
A
B
A
C
C
D
C
0
0
1
34
2
56
2
4
55
3
85
6
2
72
0
0
0
4
o5
b
20 mol% DIBAL-H
—
—
20 mol% DIBAL-H
10 mol% DIBAL-H
46
10 mol% NP2
o5
499
499
499
63
o5
499
499
499
83
0
43
96
91
6
5 mol% NP2
10 mol% NP3
—
—
0
10
11
12
13
14
15
15
96
97
9
0
0
20 mol% DIBAL-H
10 mol% DIBAL-H
5 mol% NP3
0.1 mL NP7 in IL
—
—
24
6
0
o5
10 mol% DIBAL-H
1
General: The NP-IL dispersion was washed several times with 2 mL acetonitrile each to remove the IL. The resulting material was dried under high
a
2
vacuum until a black powder was obtained, which was used as the (pre-)catalyst. Conditions: 0.2 mmol alkyne in 0.5 mL THF. [A] 50 1C, 10 bar H ,
b
2 2 2
THF. [B] 80 1C, 80 bar H , THF. [C] 30 1C, 2 bar H , THF. [D] 50 1C, 20 bar H , hexane. Trimerization as a side reaction.
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Upon the addition of 10 mol% DIBAL-H, NP7 was converted significantly lower conversion (Fig. 7). The internal alkyne
to an active hydrogenation catalyst of phenylacetylene, which phenylpropyne afforded 29% hydrogenation products, with
afforded styrene (34%) and ethyl benzene (4%) at 50 1C and 1-Z-phenyl-1-propene as the major product. The alkene a-methyl-
1
0 bar H . Traces of the [2+2+2]-cyclotrimerization products styrene showed very low conversion, which may be relevant in
2
103–108
were also formed.
DIBAL-H was observed with NP2 and NP3 (Table 4, entries 6–8 and (sterically hindered) 1,1-substituted alkenes. Nitriles, ketones
1–13, respectively). Although the conversion of phenylacetylene was or nitro compounds showed no conversion to hydrogenated
low with catalytic NP2 and NP3 at 50 1C, 10 bar H without DIBAL-H, products, probably due to irreversible catalyst oxidation by the
A similar activation by the hydride reagent the context of chemoselective hydrogenations of alkynes over
1
2
near quantitative amounts of alkane were formed after NP activation reduction-sensitive functional groups.
with DIBAL-H under the same conditions. Both hydrogenations
could also be performed under very mild conditions (2 bar H2,
Conclusions
30 1C, Table 4, entries 7, 8 and 12, 13).
The samples withdrawn after 6 h from the reaction showed
the semi-hydrogenation product styrene as the major compo-
nent compared to the final alkane ethylbenzene (Table 4,
entries 8 and 13). It is likely that the hydrogenation is a two-
step process with the semi-hydrogenation product styrene
formed first and presumably in a faster reaction step. Styrene
is then independently hydrogenated to ethylbenzene, which
takes a longer time to run to completion.
The synthesis of the Co/Al nanoalloys CoAl and the previously
unknown Co Al in nanoparticular form yielded NP diameters of
3
less than 10 nm by microwave-assisted thermal decomposition
in an ionic liquid. The dual-source precursor systems of various
organometallic cobalt and aluminum complexes in the ionic
liquid [BMIm]NTf
2
were used for the synthesis of Co/Al-NPs in
(CO) and [(AlCp*)
2 2 2 2
or [Co( Pr -MeAMD) ] and [Me Al( Pr -MeAMD)] proved to be
different ratios. The metal precursors Co
2
8
4
]
i
i
A series of alternative reductants were tested as co-catalysts
successful for the synthesis of the Co/Al nanoalloys. Whereas,
(
Tables S6 and S10, ESI†). LiAlH
to DIBAL-H; BH
ÁTHF and NaH gave lower conversions. Lower
amounts of DIBAL-H resulted in lower catalytic activities
Table S10, ESI†). In summary, the highest catalytic activity
4
showed comparable reactivity
i
the dual-source system of [Co( Pr -MeAMD) ] and [(AlCp*) ] and
2
2
4
3
2
also the single-source precursor [Cp*Co(m-H)(Al(k -(CH SiMe )-
2
2
NSiMe )(btsa))] led to the formation of monometallic Co-NPs.
3
(
However, all the products showed impurities of amorphous
aluminum species in the background of the Co/Al- or Co-NPs.
Thus, admittedly, the phase-pure synthesis of Co/Al-NPs from a
dual- or even a single-source precursor via a wet-chemical
synthetic route remains an unresolved problem. It is still a
challenge to avoid the concomitant formation of Co-NPs and
Al O . Thereby, we noted that in the only other two reports on
for the hydrogenation of phenylacetylene was achieved with the
combinations of DIBAL-H and NP2 or NP3 in THF (Table 4,
entries 7, 8 and 12, 13), respectively.
Subsequently, we explored the scope of this hydrogenation
protocol with NP3 (Fig. 7). The observed chemoselectivities were
strongly dependent on the functional groups present in the
substrates and the reaction times. Phenylacetylene, 3-methyl-
phenylacetylene and 1-octyne cleanly afforded the corresponding
alkanes. 4-Chlorophenylacetylene gave the alkene (alkene/alkane =
2
3
28
Co/Al-NPs, oxide byproducts (Al O ) or even fully oxidized
CoAlO -NPs were formed. The presence of dioxygen impurities
x
2
3
68
seems very difficult to avoid, which together with the high
oxophilicity of Co and Al metal then led to substantial oxidation
products. This oxidation may not necessarily occur during the
synthesis but during the necessary subsequent handling for
analysis, where often an even short contact with air is unavoidable.
For future work in this direction, other single-source precursors,
synthetic conditions with reducing agents (which also act as oxygen
scavengers), more stringent inert conditions also for analysis, and
protection of the Co/Al-NPs by stabilizing capping agents (which
8
: 1), but underwent no competing hydrodehalogenation. Sub-
strates with methoxy, carbonyl and amine moieties showed
may also block the access of O
We examined the catalytic properties of the as-formed Co/Al-NPs
in hydrogenation reactions. Both CoAl- (NP2) and Co Al-NPs (NP3)
2
) may be routes to follow.
3
were effective catalysts for alkyne-to-alkane hydrogenation in
the presence of DIBAL-H as a co-catalyst under mild conditions
(
2 bar H , 30 1C).
2
Further investigations can also focus on the synthesis of
further Co/E nanoalloys (E = Ga and In) and the examination of
their catalytic properties.
Fig. 7 Hydrogenation of alkynes, nitriles, ketones and nitro compounds
3
with Co Al-NPs. The NP-IL dispersion was washed several times with 2 mL
acetonitrile each to remove the IL. The resulting material was dried under
high vacuum until a black powder was obtained. Standard conditions:
5
mol% NP3 (Co
0 1C, 2 bar H
3
Al), 10 mol% DIBAL-H, 200 mmol substrate in 0.5 mL THF,
, 10 h. Yield of alkene/yield of alkane. (a) 6 h reaction time. Conflicts of interest
3
2
(b) Mixture of alkenes. (c) 5% of ketone reduction. (d) 6 h reaction time,
2
4% Z-alkene + 2% E-alkene.
There are no conflicts to declare.
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Acknowledgements
19 C. Dietrich, G. Uzunidis, Y. Tr ¨a utlein and S. Behrens,
J. Visualized Exp., 2018, 138, e58058.
This work has been supported by the German Science Foundation
2
2
0 W. T. Ralston, W.-C. Liu, S. Alayoglu and G. Melaet, Top.
Catal., 2018, 61, 1002–1015.
1 M. M. van Schooneveld, C. Campos-Cuerva, J. Pet, J. D.
Meeldijk, A. Meijerink, B. H. Ern ´e and M. F. de Groot,
J. Nanopart. Res., 2012, 14, 991–1003.
(
DFG) within the priority program SPP 1708 ‘‘Material Synthesis
Near Room Temperature’’ (grant Fi502/32-1/2 for RAF and grant JA
66/31-1/2 for CJ). The authors gratefully acknowledge technical
4
assistance by the Max-Planck-Institut f u¨ r Eisenforschung GmbH,
D u¨ sseldorf for TEM measurements.
22 M. Sankar, N. Dimitratos, P. J. Miedziak, P. P. Wells,
C. J. Kiely and G. J. Hutchings, Chem. Soc. Rev., 2012, 41,
8
099–8139.
Notes and references
2
3 D. Martin Alonso, S. G. Wettstein and J. A. Dumesic, Chem.
Soc. Rev., 2012, 41, 8075–8098.
24 R. Ferrando, J. Jellinek and R. L. Johnston, Chem. Rev.,
2008, 108, 847–910.
1
2
3
4
F. Tao, S. Zhang, L. Nguyen and X. Zhang, Chem. Soc. Rev.,
012, 41, 7980–7993.
M. Fatmi, M. A. Ghebouli, T. Chihi, S. Boucetta and
Z. K. Heiba, Rom. J. Phys., 2011, 56, 935–951.
J. Zhang, G. Chen, D. Guay, M. Chaker and D. Ma, Nano-
scale, 2014, 6, 2125–2130.
I. Favier, E. Teuma and M. Gomez, in Nanocatalysis in Ionic
Liquids, ed. M. H. G. Prechtl, Wiley-VCH, Weinheim, 2017.
H. Lindlar, Helv. Chim. Acta, 1952, 35, 446–450.
M. Garc ´ı a-Mota, J. G ´o mez-D ´ı az, G. Novell-Leruth, C. Vargas-
Fuentes, L. Bellarosa, B. Bridier, J. P ´e rez-Ram ´ı rez and
N. L o´ pet, Theor. Chem. Acc., 2011, 128, 663–673.
G. Vil ´e , N. Almora-Barrios, S. Mitchell, N. L ´o pez and J. P ´e rez-
Ram ´ı rez, Chem. – Eur. J., 2014, 20, 5926–5937.
2
25 M. Cokoja, H. Parala, A. Birkner, R. A. Fischer, O. Margeat,
D. Ciuculescu, C. Amiens, B. Chaudret, A. Falqui and
P. Lecante, Eur. J. Inorg. Chem., 2010, 1599–1603.
26 M. Cokoja, H. Parala, A. Birkner, O. Shekhah, M. W. E. van
Berg and R. A. Fischer, Chem. Mater., 2007, 19, 5721–5733.
27 M. Cokoja, H. Parala, M. K. Schr o¨ ter, A. Birkner,
M. W. E. van den Berg, W. Gr u¨ nert and R. A. Fischer,
Chem. Mater., 2006, 18, 1634–1642.
28 M. Cokoja, B. J. Jagirdar, H. Parala, A. Birkner and R. A.
Fischer, Eur. J. Inorg. Chem., 2008, 3330–3339.
29 W. Ostwald, Z. Phys. Chem., 1901, 37, 385.
30 W. Ostwald, Lehrbuch der Allgemeinen Chemie, Engelmann,
Leipzig, 1896.
31 P. S. Campbell, M. H. G. Prechtl, C. C. Santini and P.-H.
Haumesser, Curr. Org. Chem., 2013, 17, 414–429.
32 D. Freudenmann, S. Wolf, M. Wolff and C. Feldmann,
Angew. Chem., Int. Ed., 2011, 50, 11050–11060.
33 E. Ahmed, J. Breternitz, M. F. Groh and M. Ruck,
CrystEngComm, 2012, 14, 4874–4885.
5
6
7
8
S. Nishimura, Handbook of Heterogeneous Catalytic Hydro-
genation for Organic Synthesis, Wiley, New York, 2001,
p. 148.
9
M. Armbr u¨ ster, G. Wowsnick, M. Friedrich, M. Heggen and
R. Cardoso-Gil, J. Am. Chem. Soc., 2011, 133, 9112–9118.
1
0 W.-C. Liu, G. Melaet, W. T. Ralston, S. Alayoglu, Y. Horowitz,
R. Ye, T. Hurlburt, B. Mao, E. Crumlin, M. Salmeron and
G. A. Somorjai, Catal. Lett., 2016, 146, 1574–1580.
1
1 S. Alayoglu, S. K. Beaumont, G. Melaet, A. E. Lindeman,
N. Musselwhite, C. J. Brooks, M. A. Marcus, J. Guo, Z. Liu,
N. Kruse and G. A. Somorjai, J. Phys. Chem. C, 2013, 117,
34 L. Schmolke, S. Lerch, M. B u¨ low, M. Siebels, A. Schmitz,
J. Thomas, G. Dehm, C. Held, T. Strassner and C. Janiak,
Nanoscale, 2019, 11, 4073–4082.
2
1803–21809.
35 J. D. Scholten, B. C. Leal and J. Dupont, ACS Catal., 2012,
21, 184–200.
36 T. Dang-Bao, D. Pla, I. Favier and M. G o´ mez, Catalysts,
2017, 7, 207–240.
37 P. Dash, N. A. Dehm and R. W. J. Scott, J. Mol. Catal. A:
Chem., 2008, 286, 114–119.
38 C. Vollmer and C. Janiak, Coord. Chem. Rev., 2011, 255,
2039–2057.
39 H. Kaper, F. Endres, I. Djerdj, M. Antonietti, B. M. Smarsly,
J. Maier and Y.-S. Hu, Small, 2007, 3, 1753–1763.
40 M. Antonietti, D. Kuang, B. Smarsly and Y. Zhou, Angew.
Chem., Int. Ed., 2004, 43, 4988–4992.
41 D. Marquardt and C. Janiak, Nachr. Chem., 2013, 61, 754–757.
42 J. Dupont and J. D. Scholten, Chem. Soc. Rev., 2010, 39,
1780–1804.
43 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 2000,
39, 3772–3789.
44 J. Dupont, J. Braz. Chem. Soc., 2004, 15, 341–350.
45 K. Sch u¨ tte, J. Barthel, M. Endres, M. Siebels, B. Smarsly,
J. Yue and C. Janiak, ChemistryOpen, 2017, 6, 137–148.
1
1
2 S. Alayoglu, S. K. Beaumont, F. Zheng, V. V. Pushkarev,
H. Zheng, V. Iablokov, Z. Liu, J. Guo, N. Kruse and
G. A. Somorjai, Top. Catal., 2011, 54, 778–785.
3 K. Sch u¨ tte, A. Doddi, C. Kroll, H. Meyer, C. Wiktor,
C. Gemel, G. van Tendeloo, R. A. Fischer and C. Janiak,
Nanoscale, 2014, 6, 5532–5544.
1
1
4 K. Sch u¨ tte, H. Meyer, C. Gemel, J. Barthel, R. A. Fischer and
C. Janiak, Nanoscale, 2014, 6, 3116–3126.
5 M. Armbr u¨ ster, K. Kovnir, M. Friedrich, D. Teschner,
G. Wowsnick, M. Hahne, P. Gille, L. Szentmikl o´ si,
M. Feuerbacher, M. Heggen, F. Girgsdies, D. Rosenthal,
R. Schl o¨ gl and Y. Grin, Nat. Mater., 2012, 11, 690–693.
6 G. Ertl, H. Knozinger, F. Schuth and J. Weitkamp, Handbook
of heterogeneous catalysis, Wiley-VCH, Chichester, 2008.
7 P. Xi, Y. Cao, F. Yang, C. Ma, F. Chen, S. Yu, S. Wang,
Z. Zeng and X. Zhang, Nanoscale, 2013, 5, 6124–6130.
8 D. O. Silva, L. Luza, A. Gual, D. L. Baptista, F. Bernardi,
M. J. M. Zapata, J. Morais and J. Dupont, Nanoscale, 2014,
1
1
1
6, 9085–9092.
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View Article Online
NJC
Paper
4
6 A. Schmitz, K. Sch u¨ tte, V. Ilievski, J. Barthel, L. Burk,
R. M u¨ lhaupt, J. Yue, B. Smarsly and C. Janiak, Beilstein
J. Nanotechnol., 2017, 8, 2474–2483.
7 M. Siebels, L. Mai, L. Schmolke, K. Sch u¨ tte, J. Barthel,
J. Yue, J. Thomas, B. M. Smarsly, A. Devi, R. A. Fischer and
C. Janiak, Beilstein J. Nanotechnol., 2018, 9, 1881–1894.
8 C. Vollmer, R. Thomann and C. Janiak, Dalton Trans., 2012,
70 M. Luysberg, M. Heggen and K. Tillmann, J. Large Scale
Res. Facil., 2016, 2, 138.
71 A. Thust, J. Barthel and K. Tillmann, J. Large Scale Res.
Facil., 2016, 41.
72 S. Schmidt, S. Schulz, D. Blaeser, R. Boese and M. Bolte,
Organometallics, 2010, 29, 6097–6103.
73 M. P. Coles, D. C. Swenson and R. F. Jordan, Organo-
metallics, 1997, 16, 5183–5194.
4
4
4
41, 9722–9727.
9 C. Vollmer, E. Redel, K. Abu-Shandi, R. Thomann,
H. Manyar, C. Hardacre and C. Janiak, Chem. – Eur. J.,
74 J. Weßing, C. G o¨ bel, B. Weber, C. Gemel and R. A. Fischer,
Inorg. Chem., 2017, 56, 3517–3525.
2
010, 16, 3849–3858.
75 S. Wegner, C. Rutz, K. Sch u¨ tte, J. Barthel, A. Bushmelev,
A. Schmidt, K. Dilchert, R. A. Fischer and C. Janiak, Chem. –
Eur. J., 2017, 23, 6330–6340.
76 Z.-W. Fu, C.-L. Li, J. Ma, Y. Wang and Q.-Z. Qin,
J. Electrochem. Soc., 2015, 152, E50–E55.
77 M. G. Freire, C. M. S. S. Neves, I. M. Marrucho, J. A. P.
Coutinho and A. M. Fernandes, J. Phys. Chem. A, 2010, 114,
3744–3749.
5
5
0 D. Marquardt, C. Vollmer, R. Thomann, P. Steurer,
R. M u¨ lhaupt, E. Redel and C. Janiak, Carbon, 2011, 49,
1
1 R. Marcos Esteban, K. Sch u¨ tte, D. Marquardt, J. Barthel,
F. Beckert, R. M u¨ llhaupt and C. Janiak, Nano-Struct. Nano-
Objects, 2015, 2, 28–34.
326–1332.
5
5
5
5
5
5
5
5
6
6
6
6
6
2 S. Schmidt, S. Schulz and M. Bolte, Z. Anorg. Allg. Chem.,
2
009, 635, 2210–2213.
78 C. Rutz, L. Schmolke, V. Gvilava and C. Janiak, Z. Anorg.
Allg. Chem., 2017, 643, 130–135.
79 G. Beamson and D. Briggs, High Resolution XPS of Organic
Polymers, The Scienta ESCA300 Database Wiley Inter-
science, Chichester, 1992.
80 B. R. Strohmeier, Surf. Interface Anal., 1990, 15, 51–56.
81 O. B o¨ se, E. Kemnitz, A. Lippitz and W. E. S. Unger, Appl.
Surf. Sci., 1997, 120, 181–190.
82 T. Liu, Y. Pang, H. Kikuchi, Y. Kamada and S. Takahashi,
J. Mater. Chem. C, 2015, 3, 6232–6239.
83 R. Ramos, G. Cunge, P. Pelissier and O. Joubert, Plasma
Sources Sci. Technol., 2007, 16, 711–715.
84 M. C. Biesinger, B. P. Payne, A. P. Grosvenor, L. W. M. Lau,
A. R. Gerson and R. St. C. Smart, Appl. Surf. Sci., 2011, 257,
2717–2730.
85 S. N. Hosseini, T. Mousavi, F. Karimzadeh and M. H. Enayati,
J. Mater. Sci. Technol., 2011, 27, 601–606.
86 M. Ellner, S. Kek and B. Predel, J. Alloys Compd., 1992, 189,
245–248.
3 B. S. Lim, A. Rahtu, J.-S. Park and R. G. Gordon, Inorg.
Chem., 2003, 42, 7951–7958.
4 H. Li, D. B. Farmer, R. G. Gordon, Y. Lin and J. Vlassak,
J. Electrochem. Soc., 2007, 154, 642–647.
5 J. P. Coyle, W. H. Monillas, G. P. Yap and S. T. Barry, Inorg.
Chem., 2008, 47, 683–689.
6 J. Kr ¨a mer, E. Redel, R. Thomann and C. Janiak, Organo-
metallics, 2008, 27, 1976–1978.
7 E. Redel, J. Kr ¨a mer, R. Thomann and C. Janiak, J. Organomet.
Chem., 2009, 694, 1069–1075.
8 S. Sandl, F. Schwarzhuber, S. P o¨ llath, J. Zweck and A. Jacobi
von Wangelin, Chem. – Eur. J., 2018, 24, 3403–3407.
9 R. Ferraccioli, D. Borovika, A.-E. Surkus, C. Kreyenschulte,
C. Topf and M. Beller, Catal. Sci. Technol., 2018, 8, 499–507.
0 F. Michalek, A. Lagunas, C. Jimeno and M. A. Peric `a s,
J. Mater. Chem., 2008, 18, 4692–4697.
1 P. Jiang, X. Li, W. Gao, X. Wang, Y. Tang, K. Lan, B. Wang
and R. Li, Catal. Commun., 2018, 111, 6–9.
2 C. Chen, Y. Huang, Z. Zhang, X.-Q. Dong and X. Zhang,
Chem. Commun., 2017, 53, 4612–4615.
3 F. Chen, C. Kreyenschulte, J. Radnik, H. Lund, A.-E. Surkus,
K. Junge and M. Beller, ACS Catal., 2017, 7, 1526–1532.
4 P. B u¨ schelberger, E. Reyes-Rodriguez, C. Sch o¨ ttle, J. Treptow,
C. Feldmann, A. Jacobi von Wangelin and R. Wolf, Catal. Sci.
Technol., 2018, 8, 2648–2653.
87 A. A. Khassin, T. M. Yurieva, V. V. Kaichev, V. I.
Bukhtiyarov, A. A. Budneca, E. A. Paushtis and V. N.
Parmon, J. Mol. Catal. A: Chem., 2001, 175, 189–204.
88 H.
B o¨ nnemann,
W.
Brijoux,
R.
Brinkmann,
N. Matoussevitch, N. Walf ¨o fner, N. Palina and H. Modrow,
Inorg. Chim. Acta, 2003, 350, 617–624.
89 S. R o¨ sler, J. Obenauf and R. Kempe, J. Am. Chem. Soc.,
2015, 137, 7998–8001.
90 F. Chen, C. Topf, J. Radnik, C. Kreyenschulte, H. Lund,
M. Schneider, A.-E. Surkus, L. He, K. Junge and M. Beller,
J. Am. Chem. Soc., 2016, 138, 8781–8788.
91 G. Zhang, B. L. Scott and S. K. Hanson, Angew. Chem., Int.
Ed., 2012, 51, 12102–12106.
92 D. G ¨a rtner, A. Welther, B. R. Rad, R. Wolf and A. Jacobi von
Wangelin, Angew. Chem., Int. Ed., 2014, 53, 3722–3726.
93 F. Chen, A.-E. Surkus, L. He, M.-M. Pohl, J. Radnik, C. Topf,
K. Junge and M. Beller, J. Am. Chem. Soc., 2015, 137, 11718–11724.
94 Z. Wie, Y. Chen, J. Wang, D. Su, M. Tang, S. Mao and
Y. Wang, ACS Catal., 2016, 6, 5816–5822.
6
6
6
5 R. Xu, T. Xie, Y. Zhang and Y. Li, Nanotechnology, 2007,
1
8, 055602.
6 R. B. N. Baig, S. Verma, R. S. Varma and N. Nadagouda,
ACS Sustainable Chem. Eng., 2016, 4, 1661–1664.
7 L. Wang, L. Wang, J. Zhang, X. Liu, H. Wang, W. Zhang,
Q. Yang, J. Ma, X. Dong, S. J. Yoo, J.-G. Kim, X. Meng and
F.-S. Xiao, Angew. Chem., Int. Ed., 2018, 57, 6104–6108.
8 H. B u¨ rger and U. Wannagat, Monatsh. Chem., 1963, 94,
6
6
1
007–1012.
9 C. Ganesamoorthy, S. Loerke, C. Gemel, M. Winter,
P. Jerabek, G. Frenking and R. A. Fischer, Chem. Commun.,
2
013, 49, 2858–2860.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16583--16594 | 16593

View Article Online
Paper
NJC
95 R. Adam, J. R. Cabrero-Antonino, A. Spannenberg, K. Junge, 101 T. Schwob and R. Kempe, Angew. Chem., Int. Ed., 2016, 55,
R. Jackstell and M. Beller, Angew. Chem., Int. Ed., 2017, 56,
216–3220.
6 K. Tokmic, C. R. Markus, L. Zhu and A. R. Fout, J. Am.
Chem. Soc., 2016, 138, 11907–11913.
15175–15179.
3
102 R. V. Jagadeesh, K. Murugesan, A. S. Alshammari,
H. Neumann, M.-M. Pohl, J. Radnik and M. Beller, Science,
2017, 358, 326–332.
9
9
7 R. P. Yu, J. M. Darmon, C. Milsmann, G. W. Margulieux, 103 G. Dom ´ı nguez and J. P ´e rez-Castells, Chem. – Eur. J., 2016,
S. C. E. Stieber, S. DeBeer and P. J. Chirik, J. Am. Chem. Soc.,
013, 135, 13168–13184.
8 P. B u¨ schelberger, D. G ¨a rtner, E. Reyes-Rodriguez,
F. Kreyenschmidt, K. Koszinowski, A. Jacobi von Wangelin 105 N. Saino, D. Kogure and S. Okamoto, Org. Lett., 2005, 14,
and R. Wolf, Chem. – Eur. J., 2017, 23, 3139–3151. 3065–3067.
22, 6720–6739.
2
104 P. R. Chopade and J. Louie, Adv. Synth. Catal., 2006, 348,
9
9
2307–2327.
9 J. Osuna, D. de Caro, C. Amiens, B. Chaudret, E. Snoeck, 106 S. Saito and Y. Yamamoto, Chem. Rev., 2000, 100, 2901–2915.
M. Respaud, J.-M. Broto and A. Fert, J. Phys. Chem., 1996, 107 M. Lautens, W. Klute and W. Tam, Chem. Rev., 1996, 96,
1
00, 14571–14574.
00 F. K. Schmidt, Y. Titova, L. B. Belykh, V. A. Umanets and 108 N. Agenet, V. Gandon, K. P. C. Vollhardt, M. Malacria and
S. S. Khutsishvili, Russ. J. Gen. Chem., 2012, 82, 1334–1341. C. Aubert, J. Am. Chem. Soc., 2007, 129, 8860–8871.
49–92.
1
16594 | New J. Chem., 2019, 43, 16583--16594 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019