Iridium versus Iridium: Nanocluster and Monometallic Catalysts Carrying the Same Ligand Behave Differently

Article abstract of DOI:10.1002/chem.201605352

A specific secondary phosphine oxide (SPO) ligand (tert-butyl(phenyl)phosphine oxide) was employed to generate two iridium catalysts, an Ir–SPO complex and IrNPs (iridium nanoparticles) ligated with SPO ligands, which were compared mutually and with several supported iridium catalysts with the aim to establish the differences in their catalytic properties. The Ir–SPO-based catalysts showed totally different activities and selectivities in the hydrogenation of various substituted aldehydes, in which H₂is likely cleaved by a metal–ligand cooperation, that is, the SPO ligand and a neighboring metal centre operate in tandem to activate the hydrogen molecule. In addition, the supported IrNPs behave very differently from both Ir–SPO catalysts. This study exemplifies perfectly the advantages and disadvantages related to the use of the main types of catalysts, and thus the dissimilarities between them.

Full text of DOI:10.1002/chem.201605352

A Journal of
Accepted Article
Title: Iridium vs. Iridium: Nanocluster and Monometallic Catalysts
Carrying the Same Ligand Behave Differently
Authors: Israel Cano, Luis M. Martínez-Prieto, Bruno Chaudret, and
Piet W. N. M. van Leeuwen
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To be cited as: Chem. Eur. J. 10.1002/chem.201605352
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Iridium vs. Iridium: Nanocluster and Monometallic Catalysts
Carrying the Same Ligand Behave Differently
[a]
[a]
[a]
[a]
Israel Cano, Luis M. Martínez-Prieto, Bruno Chaudret, and Piet W. N. M. van Leeuwen*
Abstract: A specific secondary phosphine oxide (SPO) ligand (tert-
butyl(phenyl)phosphine oxide) was employed to generate two iridium
catalysts, an Ir–SPO complex and IrNPs ligated with SPO ligands,
which were compared mutually and with several supported iridium
catalysts with the aim to establish the differences in their catalytic
properties. The Ir–SPO based catalysts showed totally different
activities and selectivities in the hydrogenation of various substituted
immobilized on supports provide more stable catalysts by
avoiding aggregation and facilitating reusability. The synthesis of
non–supported MNPs requires the use of ligands or stabilizing
agents that provide steric and/or electronic protection to
[
9]
circumvent aggregation. Ligated MNPs have a larger potential
than homogeneous catalysts, because in addition to the ligand
modification that they share, MNPs offer a range of additional
properties that are amenable to variation, although detailed
control and characterization is less straightforward. The use of
functional ligands that participate in the catalytic process, thus
enhancing activity and selectivity, is an additional tool in catalyst
aldehydes, in which
H
2
is likely cleaved by a metal-ligand
cooperation, that is, the SPO ligand and a neighboring metal center
operate in tandem to activate the hydrogen molecule. In addition, the
supported IrNPs behave very differently from both Ir–SPO catalysts.
This study exemplifies perfectly the advantages and disadvantages
related to the use of the main types of catalysts and, thus, the
dissimilarities between them.
[
10 ]
development.
In this context, secondary phosphine oxides
(SPOs) are an interesting alternative to common tertiary
phosphorus ligands in catalysis because of their singular
[
11 ]
properties.
Indeed, their corresponding metal complexes
heterolytically through the
exhibit a particular ability to cleave H
2
metal and the oxygen atom. Subsequently, the complex can
transfer the hydrogen atoms to an appropriate, polarized
Introduction
[
12 ]
substrate as we have shown both in homogeneous
and
Catalytic transformations are of extraordinary importance and
[13]
MNP catalysis.
[1]
play a key role in industry and research. Indeed, a large variety
of catalysts have been reported for an ever increasing number of
simple and complex conversions. Metals may feature in catalysts
in several ways, the three simplest ones being: as metal ligand
complexes, nanoparticles (NPs) ligated by ligands, and metal
particles on solid supports. Single site, homogeneous catalysts
based on organometallic complexes can provide high activities
and selectivities as a result of their ease of modification and
Herein we describe that one and the same SPO ligand L leads
to different catalytic behaviour of a homogeneous hydrogenation
catalyst derived from precursor 1 and SPO–stabilized iridium
nanoparticles (IrNPs) 2, while ligand-free supported IrNPs
catalysts exhibit catalytic properties strikingly different again.
Results and Discussion
[
2 ]
control of the ligand environment.
heterogeneous catalysts are usually cheap, stable and reusable,
but their modification in systematic way is less
straightforward. The behaviour of these metal catalysts can be
On the other hand,
The treatment of (1,5-cyclooctadiene)(methoxy)iridium(I) dimer
a
(
2
[Ir(OMe)(COD)] ) with 4 equivalents of SPO L and 2 equivalents
[3]
of H O in tetrahydrofuran (THF) at room temperature (R.T.)
2
[4]
strongly influenced by the support and its acidity, but also the
affords complex 1 (Scheme 1), in which the ligand coordinates
as a hydrogen bonded pair of two SPO molecules, generating a
monoanionic bidentate ligand (see Experimental Section for
[
5]
size of the metal particle may affect activity and selectivity.
Ligands can be added to the surface and asymmetric
hydrogenation of unsaturated compounds can be achieved this
[11d,14]
details).
[
6]
way, not to mention the numerous compounds that can stick to
[7]
the surface and change the properties. Metallic nanoparticles
MNPs) are placed at the frontier between these two catalysis
(
fields and combine the advantages of homogeneous and
heterogeneous catalysts, that is, high activity, high selectivity,
[
8 ]
stability and amenability to ligand modification.
MNPs
[
a]
Dr. I. Cano, Dr. L. M. Martínez-Prieto, Dr. B. Chaudret, Prof. P. W.
N. M. van Leeuwen
Scheme 1. Formation of iridium SPO complex 1.
LPCNO; Laboratoire de Physique et Chimie de Nano-Objets
UMR 5215 INSA-CNRS-UPS
Institut National des Sciences Appliquées
The use of an iridium precursor with less labile anions, such as
dimeric chloro(1,5-cyclooctadiene)iridium, led to the formation of
a monomeric (COD)Ir(I)Cl complex with the SPO coordinated as
135, Avenue de Rangueil, 31077 Toulouse (France)
E-mail: vanleeuw@insa-toulouse.fr
Supporting information for this article is given via a link at the end of
the document.
[
11c]
the neutral acid.
2
In the present case, the addition of H O
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leads to decoordination of methoxide as methanol (MeOH) and
enables the coordination of a second molecule of SPO. After
Complex 1 was used as the precursor for homogeneous
catalysis; under H
diastereomeric dihydrides Ir((SPO)
dihydride dimers thereof after loss of a solvent molecule.
[Ir(OMe)(COD)] was also used for the formation of SPO–
2
it is converted to a mixture of three
adding H
2
O the signal corresponding to 1 appeared in the
2
H)H (solvent) and bridging
2
2
3
1
1
[ 15 ]
P{ H} NMR spectrum, as well as the characteristic absorptions
1
of MeOH in the corresponding H NMR spectrum. X-ray analysis
confirmed the structure of 1 (Figure 1, for further details see
section 3, ESI).
2
stabilized IrNPs 2. One of the most common synthetic
methodologies employed to generate IrNPs is the reduction of
2
an Ir(I) precursor with a suitable reducing agent such as H ,
[
16]
NaBH
the preparation of IrNPs ligated by asymmetric SPOs,
procedure analogous to that previously described for
4
, etc.
We chose the same protocol that was used for
[
13d]
a
[
13a,17]
RuNPs.
of [Ir(OMe)(COD)]
based on Ir) of SPO L (Scheme 2, for further details see
The IrNPs 2 were prepared at R.T. by H
2
reduction
2
in THF in the presence of 0.5 equivalents
(
Experimental Section).
2
Scheme 2. Synthesis of IrNPs 2 from [Ir(OMe)(COD)] and L.
Figure 1. X-ray structure of 1 showing thermal ellipsoids set at 40% probability
level. Hydrogen atoms have been removed for clarity.
The purified IrNPs were fully characterized by several
techniques. Transmission electron microscopy (TEM) analysis
revealed the presence of small and well-dispersed NPs with a
size ca. 1.33(0.28) nm (Figure 3, for further details see section 2,
ESI). High resolution TEM (HRTEM) images revealed crystalline
IrNPs with a face centered cubic structure (fcc). This was
confirmed by Fast Fourier Transformation (FFT) analysis carried
out on the HRTEM images in Figure 3. Wide-Angle X-ray
Scattering (WAXS) analysis confirmed the fcc structure and
indicated a coherence length of ca. 1.5 nm (Section 1, ESI).
These data agree with the average sizes determined by TEM
and prove the crystallinity of the IrNPs.
The presence of the proton in the intramolecular hydrogen bond
–
POHOP– was demonstrated by solid state fast magic angle
1
1
spinning (MAS) H NMR that allows to obtain a sharp
resonance at 16.5 ppm through elimination of the strong
homonuclear dipolar couplings (Figure 2).
H
H
1
Figure 3. a) TEM image and the corresponding size histogram of 2. b)
HRTEM image and FFT of a single particle for 2.
1
Figure 2. H fast MAS (spinning rate 35 kHz) NMR spectrum of 1 which
shows the resonance of hydrogen at 16.5 ppm corresponding to the
intramolecular hydrogen bond.
The coordination of L to the IrNP surface was demonstrated by
3
1
solid state MAS NMR spectroscopy. The
spectrum of 2 displayed broad signals centered around 68 ppm
Figure 4) which correspond to the chemical shift of coordinated
P MAS NMR
(
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3
1
ligand L (the signal of free L in the solid state P MAS NMR
spectrum occurs at 42 ppm). Elemental analysis (EA) of 2 gave
an Ir content of 47.9%, which is in good agreement with the
value measured by energy-dispersive X-ray spectroscopy (EDX,
reduction of nitroarenes to anilines has been extensively
[20,21]
described with the use of MNPs.
supported IrNPs catalysts, such as Ir/SiO
Indeed, the use of different
[22]
[23]
2
and Ir/CNT, was
reported for the hydrogenation of nitrobenzenes, leading to the
formation of anilines as major products with high activities (entry
6).
4
5.7%). EA was consistent with a metal–ligand ratio of 1.85:1. It
is worth noting that the Ir/L ratio accounts for a large amount of
ligand coordinated to the surface of the nanoparticle.
Surprisingly, we noted a decreased activity and selectivity for 1
when a nitrile group was present (entry 7). We hypothesized that
the cyano functionality poisons the catalyst by coordination to
the complex, generating an inactive species. In fact, we found
that hydrogenation of cinnamaldehyde catalyzed by 1, which
usually proceeds quantitatively, in the presence of excess
acetonitrile was completely shut down. Although we detected a
similar poisoning in the hydrogenation of terminal alkynes
catalyzed by gold nanoparticles (AuNPs) due to an
1
3b
acetylide/SPO exchange, this phenomenon was not observed
for as p-cyanobenzaldehyde was hydrogenated to the
corresponding cyanobenzyl alcohol with complete selectivity
entry 8). In contrast, the reduction of benzonitrile catalyzed by
IrNPs/Al involved the reduction of the cyano group and
dibenzylamine was generated as main product (entry 9).
2
(
2
O
3
[24]
31
Finally, of particular importance is the selective hydrogenation of
2-octynal to the corresponding propargyl alcohol catalyzed by 2,
which proceeded with very high selectivity (entry 11). This result
highlights the role of the SPO acting as heterolytic activator for
Figure 4. P MAS NMR spectra of L and IrNPs 2. * denote spinning side
bands.
2
H cooperatively with a neighbouring metal atom. Interestingly,
The catalytic activity of iridium complex 1 and IrNPs 2 was
evaluated in the hydrogenation reaction of several substituted
aldehydes and compared with the catalytic behaviour of several
iridium supported catalysts reported in literature. Table 1 shows
that there are marked differences in the catalytic behaviour of Ir–
SPO complex 1, SPO–stabilized IrNPs 2, and Ir–supported
catalysts. Complex 1 showed a very high activity and selectivity
in the hydrogenation reaction of cinnamaldehyde and the
corresponding unsaturated alcohol was generated with 99% of
selectivity (entry 1). Although the activity was lower, the IrNPs 2
maintained this ability and the aldehyde group was reduced with
analogous selectivity (entry 2), confirming the role of the SPO as
functional ligand in the heterolytic cleavage of dihydrogen. As
no reaction was observed when 1 was employed in the
reduction of this substrate (entry 10). In a control experiment
consisting in the hydrogenation of cinnamaldehyde in the
presence of 2-octynal, we found complete poisoning of catalyst
1
2
and no reaction of cinnamaldehyde was observed. In catalyst
active sites of different character may be expected. The
differences in behaviour of 1 and 2 indicate that the catalytic
activity of either of them is not due to a simple leaching or MNP
[25]
formation, a persistent issue in both fields of catalysis.
Iridium-based complexes have shown a limited efficiency in the
chemoselective hydrogenation of substituted aldehydes and only
[
26]
a few systems performing this process have been reported. In
addition, MNPs rarely produce this transformation by
[
18]
[19]
a
expected, the use of IrNPs supported on SiO
2
or MWCNTs
heterolytic cleavage mechanism involving the ligand or
stabilizing agent. Indeed, the described systems based on
(
multiwalled carbon nanotubes) involved a reduction in the
selectivity compared to Ir–SPO based catalysts (entry 3) and
both aldehyde and alkene are hydrogenated in an unselective
way. The differences in activity observed for the two Ir–SPO
based catalysts could be due to the availability of the active sites.
While the single site homogeneous catalyst 1 shows direct
access, the presence of inactive Ir atoms in the core and the
high coverage of ligand for IrNPs 2 may reduce the rate.
iridium achieve the H
2
activation by the use of heterogeneous
catalysts consisting of IrNPs immobilized on oxide supports or
[
18,19,27]
oxygenated surfaces.
To the best of our knowledge, the
Ir–SPO complex 1 and SPO–stabilized IrNPs 2 perform as the
best catalysts in terms of selectivity compared to iridium systems
[
18,19,26,27]
reported to date.
Hydrogenation of p-nitrobenzaldehyde catalyzed by 1 gave the
corresponding nitrobenzyl alcohol with perfect retention of the
nitro group (entry 4). However, the presence of an active surface
area in the IrNPs may lead to contact with both functional groups
and their subsequent reduction. When 2 was employed as
catalyst (entry 5) both aldehyde and nitro groups were
hydrogenated, affording 4-aminobenzaldehyde (5 h) or 4-
aminobenzyl alcohol (18 h) as main products and small amounts
of by-products resulting from nitro group hydrogenation, such as
azoarenes, and thus 2 shows no selectivity in this instance. The
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[
a]
Table 1. Catalytic Hydrogenation of various substrates with 1, 2 and different supported IrNPs.
[
b]
[c]
-1
Entry
Catalyst
1
Substrate
Product
S/C
P (bar)
T (ºC)
t (h)
Conversion (%)
Selectivity (%)
TOF (h )
[
d]
2.5
97
>99
99:1 (UA:A)
99:1 (UA:A)
2040
600
1
3000
5
R.T.
5
18
5
99
51
99:1 (UA:A)
98:2 (UA:A)
22
41
2
2
400
10
R.T.
[
18]
Ir/SiO
2
240
51
6.2
10
90
90
3
n.d.
21.6
50
57:40:3 (UA:Al:O)
68:17:11:4 (UA:Al:A:O)
17.3
[e]
3
4
[19]
Mixture
Ir/MWCNT
25.4
600
80
1
3000
5
R.T.
5
>99
>99
>99
[
f]
5
54
5
6
2
400
20
R.T.
1
8
>99
7
95
92
22
[
22]
Ir/SiO
2
3868
3846
3000
400
9
R.T.
25
0.5
n.d.
18
542
[
23]
Ir/CNT
20
40
40
87
>99
71
5220
28.3
11
7
8
1
2
R.T.
R.T.
17
18
>99
>99
[
g]
[h]
[
24]
298
20
20
41
78
114
66
9
Ir/Al
2
O
3
20.7
100
n.d.
[g]
[h]
746
1
0
1
1
2
no reaction
3000
400
40
40
R.T.
R.T.
18
18
0
–
–
1
80
96:4 (UA:Al)
18
[
a] Reagents and conditions: 1 (0.00125 mmol), 2 (0.0025 mmol Ir assuming % of Ir from EA), THF (0.75 mL). [b] Conversions and product identities were
1
determined by H NMR spectroscopy (average of two runs). [c] UA = Unsaturated Alcohol, A = Saturated Alcohol, Al = Saturated Aldehyde, O = other. [d]
Maximal TOF. [e] Our estimate according to the method applied in this publication. [f] 4-Aminobenzyl alcohol, azoarenes and other hydrogenation compounds as
by-products.
[
20a,28]
[g] Benzylamine and toluene as by-products. [h] Initial TOF.
Conclusions
Experimental Section
In conclusion, two Ir–SPO based catalysts, an Ir–SPO complex
and IrNPs stabilized with SPO ligands, and supported iridium
catalysts exhibit completely different selectivities and rates for a
small range of functional aldehydes. The SPO ligand plays a key
role in aldehyde hydrogenation catalysis presumably via
heterolytic cleavage of H by metal-ligand cooperation, but the
2
two catalysts behave differently towards other functionalities.
The Ir–SPO complex showed a very high activity and selectivity
General
All oxygen and moisture sensitive operations were carried out under an
argon atmosphere using standard vacuum-line and Schlenk techniques.
Solvents were purchased from Sigma-Aldrich as HPLC grade and dried
by means of an MBraun MB SPS800 purification system. Bis(1,5-
cyclooctadiene)di-μ-methoxydiiridium(I)
butyl)phenylphosphine were purchased from Sigma-Aldrich. THF-d
dried by distillation over Na/benzophenone under Ar and degassed by
three freeze, pump, and thaw cycles. Chemical shifts of H, C and P-
NMR are reported in ppm, the solvent was used as internal standard.
Signals are quoted as s (singlet), d (doublet), m (multiplet), br (broad), dd
and
chloro(tert-
8
was
1
13
31
in
the
hydrogenation
of
cinnamaldehyde
and
p-
nitrobenzaldehyde. The IrNPs ligated by SPOs were less active,
but proved to be more robust catalysts than the complex, giving
high selectivities in the hydrogenation of substrates which
poison the previous homogeneous catalyst. On the other hand,
the selectivities for supported IrNPs were generally lower and
activities varied. The present work illustrates perfectly how the
same metal and the same ligand can be used for the preparation
of different catalysts with amazingly different properties.
(
(
double doublet), dt (double triplet), ddd (double doublet of doublets), dtd
double triplet of doublets), dm (double multiplet). Determination of
accurate mass of
1
was performed by Service Commun de
Spectrometrie de Masse, Institut de Chimie de Toulouse (Toulouse,
France). Elemental analysis of 2 was performed by Kolbe (Mülheim,
Germany).
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2
[29]
Transmission Electron Microscopy (TEM)
procedures on a F with the aid of the program SHELXL97 include in
[
30]
the softwares package WinGX.
taken from International tables for X-Ray Crystallography.
The Atomic Scattering Factors were
[
31 ]
All
TEM analyses were performed at the “Toulouse characterization platform
hydrogens atoms were placed geometrically, and refined by using a
riding model.
UMS-Castaing” on
a JEOL JEM 1400 CX-T electron microscope
operating at 120 kV. TEM grids were prepared by drop-casting of the
crude colloidal solution in THF on a holey carbon-coated copper grid.
Size histograms have been built with the help of the software ImageJ.
All non-hydrogens atoms were anisotropically refined, and in the last
cycles of refinement a weighting scheme was used, where weights are
2
2
2
calculated from the following formula: w=1/[ (Fo )+(aP) +bP] where
2
2
P=(Fo +2Fc )/3.
Drawing of molecules was performed with the program ORTEP32 with
0% probability displacement ellipsoids for non-hydrogen atoms.
High Resolution Transmission Electron Microscopy (HRTEM)
[32]
4
HRTEM observations were performed at the “Toulouse characterization
platform UMS-Castaing” on a JEOL JEM 2010 electron microscope
working at 200 kV with a resolution point of 2.35 Å. FFT treatments have
been carried out with Digital Micrograph Version 3.7.4. TEM grids were
prepared by drop-casting of the crude colloidal solution in THF on a holey
carbon-coated copper grid.
Synthetic procedures
tert-Butyl(phenyl)phosphine oxide (L):
chloro(tert-butyl)phenylphosphine (200.6 mg, 1 mmol) in THF (5 mL) was
treated with degassed water (ca. 0.5 mL) at room temperature and the
A rapidly stirred solution of
31
1
progress of the reaction was followed by P{ H} NMR (ca. 5 h, no
solvent, 162 MHz, > 99 % s, 55 ppm). The solvent was removed
completely and the residue left under vacuum overnight and then dried
by azeotropic distillation with toluene (2 x 10 mL). The residue was
washed with hexane (2 x 2 mL) and then dried under high vacuum giving
Energy Dispersive X-ray Spectroscopy (EDX)
EDX analyses were performed “Toulouse characterization platform UMS-
Castaing” on a JEOL JEM 2010 electron microscope working at 200 kV
with a resolution point of 2.35 Å. TEM grids were prepared by drop-
casting of the crude colloidal solution in THF on a holey carbon-coated
copper grid.
the product as a free flowing white powder. Yield: 161 mg, 0.88 mmol,
1
8
(
8 %. H NMR (500 MHz, CDCl
3
): 7.71 – 7.61 (m, 2H, HAr), 7.57 – 7.63
1
m, 1H, HAr), 7.51 – 7.40 (m, 2H, HAr), 7.01 (d, JHP = 453.1 Hz, 1H), 1.14
d, JPH= 16.6 Hz, 9H, C(CH
PH = 453.0). H, P, P{ H} and C{ H} NMR data were consistent
with those previously reported.
(1,2,5,6-)-1,5-Cyclooctadiene][tert-butyl(phenyl)phosphinito-tert-
3
31
(
3
1
)
3
); P NMR (202 MHz, CDCl
3
): 50.59 (d,
Wide-Angle X-ray Scattering (WAXS)
1
1
31
31
13
1
J
[33]
WAXS analyses were performed at CEMES-CNRS. Samples were
sealed in 1.5 mm diameter Lindemann glass capillaries. The samples
were irradiated with graphite monochromatized molybdenum
[
K
α
butyl(phenyl)phosphinous acid]iridium (1): tert-butyl(phenyl)phosphine
(0.071069 nm) radiation and the X-ray intensity scattered measurements
oxide (72.9 mg, 0.4 mmol) and (1,5-cyclooctadiene)(methoxy)iridium(I)
were performed using
a dedicated two-axis diffractometer. Radial
dimer ([Ir(OMe)(COD)]
2
) (66.3 mg, 0.1 mmol) were dissolved in THF (16
distribution functions (RDF) were obtained after Fourier transformation of
the reduced intensity functions.
mL). 16 L of H O were then added and the solution was stirred
2
overnight. The solvent was removed under vacuum and the residue was
dissolved in a mixture ether-pentane 1:2. The resulting solution was
concentrated under vacuum and kept overnight in the freezer at -30 ºC,
Nuclear Magnetic Resonance (NMR)
1
obtaining red crystals of 2. 76 mg, 0.114 mmol, 57 %. H NMR (400 MHz,
8
1
13
31
THF-d ): 7.74 – 7.64 (m, 4H, HAr), 7.38 (td, J = 7.8, 7.3, 1.7 Hz, 4H, HAr),
H, C and P spectra were recorded at the LCC-Toulouse on Bruker
7
.34 – 7.27 (m, 2H, HAr), 4.38 (t, J = 7.0 Hz, 2H, CHCOD), 4.03 (dd, J = 8.7,
Avance 400 and 300 spectrometers.
4.7 Hz, 2H, CHCOD), 2.15 – 1.99 (m, 2H, CH2(COD)), 1.96 – 1.83 (m, 2H,
3
CH2(COD)), 1.64 – 1.49 (m, 2H, CH2(COD)), 1.32 (d,
C(CH
JPH= 13.3 Hz, 18H,
Magic Angle Spinning Solid State NMR (MAS-NMR)
31
1
8
13
1
3
)
3
); P{ H} NMR (162 MHz, THF-d ): 88.72 (s); C{ H} NMR
8
(
(
100 MHz, THF-d ): 142.0 (m, virtual, JPP (approx.) = 23 Hz, 
approx.) = 0.008 ppm, JPC (approx.) = 45.6 Hz, CAr), 131.0 (t, JPC= 4.2
Solid-state NMR experiments were recorded at the LCC (Toulouse) on a
Bruker Avance 400 spectrometer equipped with 3.2 mm probes. Samples
Hz, CAr), 129.5 (s, CAr), 128.3 (t, JPC= 4.3 Hz, CAr), 88.3 (t, JPC = 3.3 Hz,
CHCOD), 71.3 (t, JPC = 8.6 Hz, CHCOD), 40.8 (m, virtual, JPP (approx.) = 23
Hz,  (approx.) = 0.008 ppm, JPC (approx.) = 35.0 Hz, C(CH
were spun between 16 to 20 kHz at the magic angle using ZrO
2
rotors.
31
P MAS experiments were performed with Hahn-echo synchronized with
3
)
3
), 37.0 (t,
31
the spinning rate (20 kHz) and a recycle delay of 20 s. P spectra were
recorded under high-power proton decoupling conditions. Chemical shifts
J
PC = 1.9 Hz, CH2(COD)), 28.2 (t, JPC = 2.5 Hz, CH2(COD)), 27.0 (br s,
+
3 3
C(CH ) ); ESI- Accurate mass [M+H] : Calc. 665.2284, Obs.: 665.2300,
error = 2.4 ppm.
1
31
for H are relative to TMS. P chemical shifts were referenced to an
external 85% H PO sample.
3
4
Synthesis of stabilized Ir nanoparticles 2: L (18.2 mg, 0.1 mmol) was
dissolved in THF (10 mL), and the solution was transferred via cannula to
X-ray Crystal Structure Determinations (CCDC: 1508600)
a
Fischer–Porter reactor containing
cyclooctadiene)di-μ-methoxydiiridium(I) (66.2 mg, 0.1 mmol) in THF (60
mL). The reactor was pressurized with 3 bar of H and vented twice. The
reactor was then pressurized with 5 bar of H and the reaction mixture
a
solution of bis(1,5-
Crystals of 1 were obtained by slow diffusion of hexane in a DCM
solution of 1 at -20 ºC. The measured crystal was prepared under inert
conditions immersed in perfluoropolyether as protecting oil for
manipulation.
Data were collected at the LCC-Toulouse at low temperature (100 K) on
a Bruker Kappa Apex II diffractometer using a Mo-K radiation (=
2
2
was vigorously stirred overnight at room temperature. The color of the
solution turned from yellow to black. The hydrogen pressure was
eliminated and the solvent was removed under vacuum. The IrNPs were
precipitated and washed with methanol (2 x 40 mL) and dried under
0.71073 Å) micro-source and equipped with an Oxford Cryosystems
31
Cryostream Cooler Device. The structures have been solved by Direct
vacuum. P MAS NMR: 68 ppm; Elemental analysis (%): Ir, 47.86; P,
.17; EDX (%): Ir, 45.72; P, 4.27.
[
29]
Methods using SHELXS97,
and refined by means of least-squares
4
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Catalytic hydrogenation
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Entry for the Table of Contents
FULL PAPER
Three catalysts were compared: an Ir–
SPO complex (Secondary Phosphine
Oxide), an Ir nanoparticle ligated with
the same SPO, and supported Ir
Israel Cano, Luis M. Martínez-Prieto,
Bruno Chaudret, and Piet W. N. M. van
Leeuwen*
metallic catalysts. They show
a
Page 1 – Page 7
completely different behavior in the
Iridium vs. Iridium: Nanocluster and
Monometallic Catalysts carrying the
same Ligand behave differently
hydrogenation
aldehydes.
of
functionalized
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