Fluoro-tagged osmium and iridium nanoparticles in oxidation reactions

Article abstract of DOI:10.1016/j.tet.2018.10.040

Osmium and iridium metal nanoparticles were supported on a fluorous organic-inorganic hybrid material prepared by the sol-gel process. Moreover, we also found that the thermolysis of the Ir₄(CO)₁₂ cluster in simply diphenylether also

Full text of DOI:10.1016/j.tet.2018.10.040

Accepted Manuscript
Fluoro-tagged osmium and iridium nanoparticles in oxidation reactions
Lynay Santacruz, Silvia Donnici, Albert Granados, Alexandr Shafir, Adelina Vallribera
PII:
S0040-4020(18)31246-8
10.1016/j.tet.2018.10.040
TET 29873
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 12 July 2018
Revised Date: 15 October 2018
Accepted Date: 16 October 2018
Please cite this article as: Santacruz L, Donnici S, Granados A, Shafir A, Vallribera A, Fluoro-
tagged osmium and iridium nanoparticles in oxidation reactions, Tetrahedron (2018), doi: https://
doi.org/10.1016/j.tet.2018.10.040.
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Fluoro-tagged osmium and iridium
nanoparticles in oxidation reactions
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a,b
a
a,c
Lynay Santacruz, Silvia Donnici, Albert Granados,
a*
a,c*
Alexandr Shafir and Adelina Vallribera
a
Department of Chemistry, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193 Barcelona,
Spain.
b
Department of Chemistry, Universidad de Nariño, sede Torobajo, Pasto, Colombia.
c
Centro de Innovación en Química Avanzada (ORFEO-CINQA)

1
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Tetrahedron
journal homepage: www.elsevier.com
Fluoro-tagged osmium and iridium nanoparticles in oxidation reactions
a,b
a
a,c
a*
a,c*
Lynay Santacruz, Silvia Donnici, Albert Granados, Alexandr Shafir and Adelina Vallribera,
a
Department of Chemistry, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193 Barcelona, Spain.
Department of Chemistry, Universidad de Nariño, sede Torobajo, Pasto, Colombia.
b
c
Centro de Innovación en Química Avanzada (ORFEO-CINQA)
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Osmium and iridium metal nanoparticles were supported on a fluorous organic-
inorganic hybrid material prepared by the sol-gel process. Moreover, we also found
that the thermolysis of the Ir (CO) cluster in simply diphenylether also gave Ir(0)
nanoparticles. All the materials were studied as catalysts in oxidation processes.
Fluoro-tagged iridium nanoparticles were particularly active in aerobic oxidation
processes, whereby the catalytic activity could be greatly enhanced through a simple
pre-activation procedure. With this material, benzylic alcohols could be oxidized
4
12
Available online
under O balloon in the absence of a basic additive; the oxidative stopped selectively
to the corresponding benzaldehyde. Promisingly, the same reaction conditions were
used in a benzylic CH oxidation of xanthene.
2
Keywords:
metallic nanoparticles
osmium
iridium
sol-gel
oxidation process
2
009 Elsevier Ltd. All rights reserved.
1
. Introduction
NPs assemblies into superstructures using previously stabilized
Au NPs by the protein wheat germ aggutinin (WGA-Au NPs).
4
Metal nanoparticles (M NPs) have been the subject of
The Cai’s group described the use of a fluorous pyrrolidine imide
intensive study due to their important size-dependent functional
attributes. Several approaches are used for the preparation of M
NPs, with some of the most common consisting in chemical and
electrochemical reduction or thermal decomposition of a metal
salt, metal vapour deposition, as well as photolysis and
sonochemical decomposition of metal complexes or salts. The
most used method is the chemical reduction of a metal salt in the
presence of a suitable stabilizer employed to prevent cluster over-
agglomeration and the formation of bulk metal. At the time of
our group’s entry into this field, the heavily fluorinated
compounds did not seem suitable as stabilizers for metallic
nanoparticles. Since then, we and other groups have designed and
used different type of stabilizers containing polyfluorinated
chains. Among them we want to emphasize the employment of
triblock-type fluoroalkylated oligomers ([R -(M) -R ], R :
5
as stabilizer of palladium nanoparticles. In addition, structured
semifluorinated polymer ionic liquids form fluorous
compartiments, that have been used for the preparation of Au and
6
Ag NPs. More recently, the spontaneous self-organization of
dissimilar ligands (hydrogenated (H-) and fluorinated (F-)) on the
19
surface of gold nanoparticles was studied by F NMR
7
experiments and multiscale molecular simulations.
Our work in this field began with the preparation of Pd NPs
using discrete polyfluorinated compounds as stabilizers. Thus, in
a 2002 publication, M. Moreno-Mañas et al. reported that several
simple organofluorine species were efficient in preventing Pd
8
nanoparticles agglomeration. We later discovered that certain
1
5-membered olefinic macrocycles bearing three fluorous chains
9
were also good stabilizers for Pd NPs. Further development of
the concept, however, required the design of new stabilizers,
which would be easier to prepare. We envisaged that the features
that could enhance the stabilizing effects should be: (i) presence
of long polyfluorinated chains; (ii) the sterical bulk, and (iii)
presence of potentially coordinating donor atoms. Based on these
criteria, we prepared some star-shaped fluorous aromatic
F
n
F
F
perfluorinated chain), which aggregate in aqueous or organic
media, and were shown to stabilize Au, Cu, Fe NPs. The use of
perfluorinated amphiphiles (HS-R -PEG) for the preparation of
water soluble Au NPs, as well as the study of dendrimers
1
F
2
containing
perfluorinated
shells
(from
perfluorinated
alkenethiols) to encapsulate Ag NPs in perfluorinated solvents
have also been described. Moreover, the group of Zhu reported
3
10
sulfurs. We demonstrated that, despite that heavily fluorinated
compounds are not expected to be the best constituents for
protecting shields due to the very small attractive interactions
the use of fluorous-tagged molecules for the construction of Au

2
Tetrahedron
MA(1
toward other materials and among themselves
A
, t
C
he
C
y s
E
ta
P
bi
T
liz
E
e
D
M
N
5
U
eq
S
ui
C
v)
R
inIP
a standard water-methanol mixture under NH4F
T
Nps. Then, we considered adapting such materials for use in
heterogeneous catalysis. In particular, we were intrigued by the
idea of immobilizing these M NPs on fluorours silica gel by
taking of the possible fluorous-fluorous interactions. In a
subsequent study, the catalyst recycling was performed with the
nanoparticles contained within a fluorous silica and using the
Mizoroki-Heck coupling between iodobenzene and methyl
catalysis proved unsuccessful, as did the tests employing the
formic acid as both solvent and catalyst. However, very efficient
sol-gel formation was achieved using a trifluoroacetic acid-based
18
approach described by Sharp et al., affording the homogeneous
material 1 (Scheme 2, Figure 1) after a 5 days ageing period; the
incorporation of the fluorous stabilizer was confirmed by
13a
elemental analysis (0.441 mmol of ligand per g of 1).
11
acrylate as the model system. The supported catalyst was reused
4 consecutive cycles without loss of activity with the catalyst
recovered each time via centrifugation. Control experiments, by
Material 1 was subsequently applied as a stabilizer to the
synthesis of osmium nanoparticles. Previously, the formation
of such nanoparticles has been promoted by diverse types of
1
19
F NMR, of the crude mixture after filtration of the catalyst were
chemical
entities,
including
the
1i9onic
liquid
the 4-(2-
also carried to assess whether leaching of the palladium fluorous
stabilizer could take place. In an effort to create a more robust
catalyst, we envisioned the synthesis of an hybrid material with
the stabilizer linked covalently to the silica gel matrix, 1. The
idea, in fact, was not completely new, given prior work by
Bannwarth et al on the adsorption of palladium(II) complexes
containing perfluoro-phosphine ligands on FSG. We essayed
fluorous material 1 as stabilizer for metal nanoparticles (Pd, Ru,
Rh) with excellent results (Scheme 1; a, b and c). The Pd@1
resulted a valuable tool for facilitating the recovery and reuse of
the expensive metal in palladium catalyzed cross-coupling
reactions that were carried out under aerobic and phosphine free
conditions as Mizoroki-Heck, Sonogashira and Suzuki-
Miyaura. The catalytic properties of Rh@1 and Ru@1 were
tested in the hydrogenation of arenes, a process of high industrial
interest. We found that Rh@1 catalyzes the quantitative
hydrogenation of aromatic compounds such as benzene, toluene,
styrene, phenol and pyridine at mild conditions, whereas Rh@1
butyl(methyl)imidazolium tetrafluoroborate,
hydroxyethyl)-1-piperazineethanesulfonic acid or by cetyl
trimethyl ammonium bromide. Several groups also reported
the preparation of Os(0) nanoclusters supported on carbon
nanotubes, zeolite, silica, and on graphene. We found
that Os@1 nanoparticles could be easily prepared by the
reduction of OsCl 3H O in THF using LiEt BH
20
21
22
23
24
25
12
.
3
2
3
(
superhydride) at room temperature for 2 hours (Scheme 1, d).
The new nanoparticles were found to be uniformly small and
disperse, with a Ømean = 1.3 0.2 nm as determined by TEM
Figure 2a). The electron diffraction rings obtained for this
±
(
13
14
material were indexed to the (101), (102), (110) and (201)
crystallographic planes of the hexagonal close-packed
structure (see SI). Similarly, the power X-ray diffraction
(pXRD) measurements showed the pattern expected for the
15
16
o
metallic hexagonal osmium (2θ = 43.5 , corresponding to the
metal (101) plane (see SI). Multiplex spectra corresponding to
F1s, Os4f and Si2p were obtained through XPS studies of a
sample of Os@1 (see SI).
17
was less active.
Herein, we report our recent results on the synthesis and
characterization of fluoro-tagged iridium and less common
osmium nanoparticles using material 1 as stabilizer (Scheme 1)
and its uses as catalysts in oxidation reactions.
SiO
2
Si(OEt)
3
O
O
O
Cl
Cl
N
H N(CH2)3Si(OEt)3
DIPEA
HN
N
2
Si
HSR,DIPEA
1
5-18 equiv Si(OEt)
4
N
N
N
N
N
N
THF, 0 o
Cl
C
CH
80 o
96%
3
CN
F3CCOOH, 5 days
HN
Cl
N
RS
SR
C
RS
SR
.
RuCl3 1.5H2O
100%
N
N
2
3
c)
4
RS
N
SR
1
, NaBH4, H2O
2 2 8 17
R = (CH CH )C F
d)
.
1
OsCl3 3H2O
b)
This work
.
1, NaBH4, H2O
RhCl3 3H2O
Scheme 2. Preparation of fluorinated organic-inorganic hybrid
material 1
1, LiEt3BH, THF
SiO2
O
O
O
This work
e)
a)
Si
. 1, MeOH, 60 o
1, diphenyl ether
1
2
C
Na2Pd2Cl6
HN
Ir4(CO)12
o
. NaOAc
210 C, 29h
N
N
C8F17
C8F17
S
N
S
M@1
M (0) = Pd, Rh, Ru, Os, Ir
:
Scheme 1. Preparation of materials M@1: a-c illustrate previous
results, while d and e show new work.
Figure 1. Images: a) gel 1 after ageing (5 days); b) gel 1
isolated; c) material 1 after drying.
2
. Results and discussion
As part of the same study, the formation of iridium
nanoparticles was investigated. It is important to note that most
of the reported syntheses of Ir NPs involve the reduction of an
iridium salt by the appropriate reducing agent in the presence of
the stabilizer. Following this approach, Ir NPs have been
prepared using a variety of iridium precursors, most commonly
The full details on the synthesis of the stabilizer 1 have
13a
already been described by our group elsewhere. Briefly, the
synthesis of 1, took advantage of a controlled stepwise
nucleophilic aromatic substitution to the 2,4,6-trichloro-1,3,5-
triazine core. Specifically, selective substitution of two out of
three chlorine atoms of cyanuric chloride, 2, with the thiol
F C CH CH SH could be achieved at 0 ºC. The remaining
26
27
IrCl ·H O and H IrCl ·H O. Another suitable method is the
3
2
2
6
2
17
8
2
2
so-called “organometallic approach” starting with the Ir olefin
chlorine atom was replaced with the commercially available
bifunctional sylilated amine linker (Scheme 2), affording the
target tri-substituted 4 in 97% yield. As we described earlier,
initial attempts to carry out the co-gelification of 4 with Si(OEt)4
2
8
29
complexes as 30for example [Ir(cod)Cl] ,
Ir(cod)(meCp),
2
31
[
Ir(OMe)(cod)]2
and Ir(cod)(acac) . In what could be
considered a variation on the latter approach, the synthesis of
iridium nanoparticles was also performed via the thermolysis of

3
the tetrairidium dodecacarbonyl cluster (Ir (C
A
O
C
)
C
)
E
in
P
a
T
h
E
ig
D
h- MAba
N
tch
U
es
S
o
C
f t
R
he
I
I
P
r@
T
1 materials following the same conditions.
4
12
31
boiling ionic liquid. Given the unsatisfactory results obtained in
the preparation of Ir@1 with previously assayed methodologies,
the latter thermolysis method drew our attention. For these tests,
the diphenyl ether was chosen as a reaction medium, given its
boiling point of 259 ºC, which we hoped would be sufficient for
the decarbonylative thermolysis of the Ir carbonyl clusters. In a
a
Entry
Ir % w/w
Average particle
size (nm)
1
2
3
4
5
6
7
8
14.6
22.7
16.0
17.0
20.1
20.1
17.7
15.8
1.1 ± 0.2
0.5 ± 0.2
1.1 ± 0.2
1.2 ± 0.3
0.9 ± 0.2
0.8 ± 0.2
1.0 ± 0.2
1.4 ± 0.4
typical experiment, the Ir (CO) cluster was first dissolved under
4
12
nitrogen atmosphere in diphenyl ether (DPE) (heating at 90 ºC
for 1.5 hours to improve solubility). Then, the stabilizer 1 was
added and the solution was heated up to 210 ºC for 29 hours
(Scheme 1, e). The decomposition of the cluster was followed by
IR spectroscopy, with the gradual decrease in the intensity of a
-
1
carbonyl absorption band at 2058 cm , until its full
disappearance, which was used as a sign that the reaction had
reached completion. The procedure afforded a dark material
containing Ir nanoparticles with Ømean = 0.5-1.4 nm. The protocol
was repeated multiple times, affording reproducibly batches of
nanoparticles with Ir content between 14.6-22.7 % w (Figure 2b,
Table 1). X-ray powder diffractometry revealed the presence of
a
Molar relation of metal to stabilizer 1 (1:1) in all the cases
(Figure 3); the pXRD analysis confirmed, once again, the
presence of the fcc Ir(0) phase. Given an apparent lack of a
stabilizing additive, we went on to further probe the nanoparticle
composition. The material was found to contain 23 % w in Ir
(ICP analysis), with the rest consisting of organic matter,
o
fcc Ir(0) with the presence of a peak at 2θ = 40.6 corresponding
to the metal (111) plane. Elemental analysis (17.7 % Ir and
13
4
2.5% of C), IR spectrum and solid C NMR of the batch
corresponding to entry 7 of Table 1, confirmed the presence of
the hybrid organic-inorganic matrix. Based on the % Ir content,
the yield of this sample of Ir@1 (entry 1, Table 1) was calculated
to be 93%. Multiplex spectra corresponding to F1s, Ir4f, Si2p,
C1s were obtained through XPS studies of a sample of Ir@1.
attributed as stemming from the Ph O used during the synthesis
(Scheme 3). Indeed, the solid state C CP-MAS NMR spectrum
2
1
3
of this material, which we denote as Ir@DPE, contained signals
1
3
which could be matched to those present in the C NMR
spectrum of pure Ph O (Figure 3). We are currently unsure of the
2
2
The new material presented a surface area of 14.5 m /g (BET)
mode by which diphenylether could stabilize
a
metal
and was found to be stable for over four months according to the
TEM images.
nanoparticle, given that, beyond the weakly donating oxygen, the
Ph O lacks any feature typically associated with an effective
2
nanoparticle stabilizer. We speculate that the stabilization might
involve an activation of the aromatic CH group ortho to the
oxygen; in that respect, we note the formation of small amounts
of dibenzofuran observed in the GC-MS trace of the mother
liquor of the reaction mixture. Even in the experiments with 1 as
a) HRTEM image of Os@1:
support and stabilizer of Ir Nps (using Ph O as solvent),
2
13
incorporation of Ph O was observed by solid state C CP-MAS
2
NMR spectrum of material Ir@1 (see SI). The new material
2
presented a surface area of 7.0 m /g (BET).
O
Ir(CO)3
DPE =
b) HRTEM images of Ir@1:
(OC)3Ir
Ir(CO)3
CO)3
Ir@DPE
o
Ir
210 C; - CO
(
Scheme 3. Formation of Ir NPs via thermolysis of Ir (CO) in
4
12
Ph O.
2
Figure 2. HRTEM images
As has been mentioned, the method was highly reliable for
the preparation of the Ir NPs (Table 1). Less reproducible
results were obtained in the case of Os NPs.
During the course of the preparation of the Ir NPs via the
thermolysis of the Ir (CO) cluster, we were surprised to find
4
12
that Ir NPs were formed even in the absence of a fluorous
stabilizer, i. e. simply by heating Ir (CO) in Ph O. The reaction
produced nanoparticles with a mean particle size of 0.5-1.3 nm
Table 1. Reproducibility results in the synthesis of different
4
12
2
13
Figure 3. HRTEM image of Ir@DPE; C CP-MAS NMR of
1
3
Ir@DPE (green) vs the C NMR of Ph O (brown).
2

4
Tetrahedron
ACCEPTED MAco
N
rre
U
sp
S
on
C
di
R
ngIPal
T
dehydes 6a and 6b were obtained in 85% and
9
0%, respectively (entries 14-15, Table 2 and Scheme 4),
In the process of exploring the chemical reactivity of the
indicating that, at least for these substrates, Ir@1 was a more
effective catalyst than Ir@DPE.
newly prepared Os and Ir NPs, we tested their ability to promote
the aerobic oxidation of alcohols.
The recycling of the Ir NPs proved difficult, given that both
Ir@1 and Ir@DPE are very fine powders difficult to filter or
centrifuge. After five centrifugation cycles we were able to
recover Ir@DPE, and this catalyst, once pre-heated, was as
effective as in the first run (entry 15, Table 7). No agglomeration
of nanoparticles was observed after the first run and the average
particle size was found to be 0.5-1.3 nm (by TEM). While
supporting the concept, obviously, the recycling procedure was
not operationally practical.
Scheme 4. Aerobic metal-catalyzed oxidation of benzyl
alcohols
Thus, we proceeded to test the Os- and Ir-based materials in
the aerobic oxidation of the benzylic alcohol. Regarding the
former, indeed, S. Özkar et al. have demonstrated that zeolite-
Y-based Os Nps could be successfully employed in the aerobic
oxidation of alcohols under mild conditions (2 mol% Os, 80 ºC
The Ir NPs were also tested in the aerobic benzylic oxidation
of xanthene. The reaction proved somewhat sluggish, and, as
seen in the oxidation of alcohols, the catalytic activity of Ir@1
was superior to that of Ir@DPE (Scheme 5). Thus, after approx.
32
1
week at 100 ºC under a balloon of O the use of Ir@1 (1.3
2
and 1 atm of O ). In this protocol, however, the recycling studies
2
mol% Ir) led to a quantitative formation of the target 8; only 64%
of 6 was obtained using Ir@DPE.
with this material showed the loss of activity in the second run.
Herein we describe the use of fluoro-tagged osmium
nanoparticles Os@1 as active catalysts in aerobic oxidation of
benzyl alcohol, 5a, to benzaldehyde, 6a (Scheme 4). The
experiments were conducted using a Fischer-Porter vessel in
toluene under O at 80 ºC and in the absence of any added base.
2
A control experiment in the absence of catalyst and at 0.5 atm O2
overpressure only led to traces of benzaldehyde (entry 1, Table
2
). In contrast, moderate yields of 6a were achieved using 1
Scheme 5. Ir NPs catalyzed aerobic CH oxidation of xanthene
mol% Os at 0.5-2.5 atm of oxygen (entries 2-3, Table 2). Some
improvement in yield could be achieved by raising the
temperature and the amount of catalyst loaded, leading to an 87%
yield of 6a (entries 4-5, Table 2). However, the recycling of the
catalyst showed a substantial loss of activity in the second run
As conclusion, fluoro-tagged Os and Ir NPs have been
prepared, demonstrating once more, the ability of fluorous hybrid
organic-inorganic silica to support and stabilize metal NPS. In
adittion, thermolysis of the Ir (CO) in diphenyl ether gave Ir(0)
(down to 38%, entry 5). Next, same oxidation process was tested
4
12
using the Ir@1 material as catalyst. During preliminary tests, we
noticed that benzaldehyde was obtained only in a moderate 50-
Nps. We have shown that Os and Ir NPs could catalyze aerobic
oxidation of benzyl alcohols. Particularly effective was found to
be the iridium nanoparticles Ir@1, whereby the catalytic activity
could be greatly enhanced through a simple pre-activation
procedure. With this material, benzylic alcohols could be
6
0% yield even after two days at 100 ºC in toluene and under a
balloon of O (entry 6, Table 2). Suspecting that the low catalytic
2
activity might be due to the presence of absorbed species on the
surface of a nanoparticle (such as residual CO), we introduced a
pre-activation step, whereby the Ir@1 material was subjected to
heating prior to a catalytic run. Such catalyst reactivation is not
oxidized under O balloon in the absence of a basic additive; the
2
oxidation stopped selectively at the corresponding benzaldehyde.
Promisingly, the same reaction conditions were used in a
benzylic CH oxidation of xanthene. The presence of the fluorous
stabilizer 1 was found to be crucial for the catalytic activity, with
inferior catalytic performance achieved using material Ir@DPE
lacking this stabilizer.
33
uncommon (including preheating of a M NPs under H2).
Indeed, pre-heating the catalyst to 135 ºC proved effective, with
the subsequent aerobic oxidation of benzyl alcohol (1.33 mol%
Ir, a balloon of O ) affording excellent yields of benzaldehyde
2
after 23 h (entries 7-8, Table 2); inferior results were achived
using Ir@1 activated at 200 ºC (entries 9-10). In fact, a 2 hours
pre-heating to 135 ºC proved sufficient, as represented by the
9
6% yield recorded in entry 7 of Table 2. An analysis by TEM of
nanoparticles pre-heated at 135 ºC indicated the presence of well
dispersed spherical nanoparticles of an average diameter among
0
.5-1.3 nm. No agglomeration was observed. It should also be
noted that the optimized reaction could be conducted using less
solvent (at 3M), leading to a 97% of the target aldehyde 6a (entry
1
1, Table 2). Two additional primary benzyl alcohols were also
selectively oxidized to the aldehydes under the optimized
conditions (entries 14 and 15, Table 2). The oxidation of 5b (p-
methyl) and 5c (p-NO ) gave the aldehydes in 89 and 98 % yield
2
respectively (entries 12 and 13, Table 2). The oxidation of 5a and
5
b was also tested using the material Ir@DPE obtained
previously via thermolysis of Ir (CO) in diphenyl ether. Once
4
12
again, pre-heating the nanoparticles to 135 ºC proved beneficial
for the catalytic activity. Under the optimized conditions the

5
Table 2. Tested conditions of Os and Ir NPs
A
as
C
ca
C
tal
E
ys
P
ts
T
in
E
a
D
ero
MANUSCRIPT
bic
o
xid
at
io
n o
f
benzyl alcohols via Scheme 4
Entry Alcohol M NPs cat. Mol % cat
Pre-
Pressure
T (ºC) T (h) Yield (%)
activation
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5b
5c
5a
5b
-
-
-
0
.5 atm
80
20
20
20
15
15
23
23
23
23
23
23
12
74
23
12
3
Os@1
Os@1
Os@1
Os@1
Ir@1
Ir@1
Ir@1
Ir@1
Ir@1
Ir@1
Ir@1
Ir@1
1
No
No
No
No
No
0.5 atm
2.5 atm
2.5 atm
2.5 atm
80
63
1
1
2
80
75
100
100
100
100
100
100
100
100
100
100
100
100
84
87/38
61
1
.3
.3
.3
.3
.3
.3
.3
.3
.3
.3
O
O
2
2
balloon
1
1
1
1
1
1
1
1
1
135 ºC/2h
balloon
96
135 ºC/22h
200 ºC/2h
200 ºC/22h
135 ºC/2h
135 ºC/2h
135 ºC/2h
135 ºC/2h
135 ºC/2h
O
2
2
balloon
balloon
91
O
86
0
1
2
3
4
5
O
O
O
O
O
O
2
2
2
2
2
2
balloon
balloon
balloon
balloon
balloon
balloon
59
97
89
98
Ir@DPE
Ir@DPE
85
90/90
.
.
precipitate was filtered of and was washed with toluene to afford
60 mg Ir@1 (93% yield). Analysis found: 17.7 % Ir; 42.5 % C.
Average particle diameter: 0.5-1.4 nm (based on TEM). XRD:
3
3
. Experimental section
o
2
4
0.6 (2θ). BET: 14.50 m /g.
3
.1. General methods
3
.2.4. Iridium nanoparticles stabilized by diphenyl ether
HR-TEM analyses were performed in the “Servei de
Ir@DPE: A 25 mL round-bottom flask was charged with
Ir (CO) (100 mg, 0.09 mmol) and diphenyl ether (5 mL). The
mixture was left stirring first at 90 ºC for 24 h and then heated to
10 ºC for 29 h. The precipitate was isolated by filtration and was
washed with toluene to afford 280 mg of Ir@DPE (91% yield).
Microscòpia” of the Universitat Autònoma de Barcelona, in a
JEOL JEM-2010 model at 200 kV. Os and Ir analyses were
performed in the “Servei d’Anàlisi Química” (SAQ) at the
Universitat Autònoma de Barcelona.
4
12
2
3
.2. General preparative methods
Analysis found: 22.7 % Ir; 45.4 % C. Average particle diameter:
o
2
0
.5-1.3 nm (based on TEM). XRD: 40.6 (2θ). BET: 6.90 m /g
3
.2.1. Preparation of material 1: Trifluoroacetic acid (1.8 mL)
3
.2.5. Typical procedure for oxidation of alcohols with Os@1:
was added to a vial containing the fluorinated monomer 2 (300
A mixture of benzyl alcohol (208 µL, 218 mg, 2 mmol) and
Os@1 (60 mg, 2%) in toluene (10 mL) was charged on a Fischer-
Porter reactor. We purged three times (pressurizing/
depressurizing cycles) with oxygen and then left at 2.5 atm for 15
h at 100 ºC. Upon cooling to room temperature, the reaction
mg, 0.24 mmol) and Si(OEt) (767 mg, 3.61 mmol, 15.1 eq). The
4
mixture was stirred manually to assure homogeneity and was left
undisturbed at room temperature. After 2 h, gelation was
observed. After a 5-day ageing period, the resulting gel was
crushed to a fine powder and was washed successively three
times with each of the following solvents: CH Cl , water, EtOH,
mixture was filtered through celite using CH Cl and dried to
2
2
2
2
give the benzaldehyde (182 mg, 87 % yield).
and, finally, Et O. The product was dried overnight in a vacuum
2
oven at 80 ºC affording 500 mg of a light-orange solid. Anal.
Found (in two separate analyses): C, 14.02 and 14.29; H, 1.27
and 1.30; N, 2.47 and 2.46.
3
.2.6. Typical procedure for oxidation of alcohols with Ir@1
o
or Ir@DPE: Ir@1 was activated by heating at 135 C during 2
hours. Then, a mixture of benzyl alcohol (310 µL, 323 mg, 3
mmol) and preactivated Ir@1 (46 mg, 1.3 mol%) in toluene (1
mL) was charged into a reactor tube. We purged three times
pressurizing/ depressurizing cycles) with oxygen and left for 23
h at 100 ºC under an oxygen atmosphere (balloon). Upon cooling
to room temperature, the reaction mixture was filtered through
3
.2.2. Fluoro-tagged osmium nanoparticles Os@1: A 25 mL
round-bottom flask was charged with material 1 (63 mg) and
(
anhydrous THF (10 mL) under nitrogen atmosphere. OsCl .3H O
3
2
(16 mg, 0.5 mmol) was added under vigorous stirring and then a
solution of LiB(C H )H (7 mL, 1M in THF) was slowly added.
2
5
celite using CH Cl and dried to give the benzaldehyde (305 mg,
7 % yield).
The resulting mixture was left stirring during 2 hours. The solid
was centrifugated and then washed with EtOH, water, and
acetone successively. A black solid was obtained. Osmium
content: 11 %. Average particle diameter: 1.3 ± 0.2 nm (based on
2
2
9
Acknowledgments
o
TEM). XRD: 43.5 (2θ).
We are thankful for financial support from Spain’s MICINN
3
.2.3. Fluoro-tagged iridium nanoparticles Ir@1: A 25 mL
(
Grants CTQ2014-53662-P and CTQ2017-86936-P) and MEC
(CTQ2016-81797-REDC). The DURSI-Generalitat de Cataluña
2017-SGR465) is also acknowledged.
round-bottom flask was charged with Ir (CO) (100 mg, 0.09
4
12
mmol) and diphenylether (5 mL). The mixture was left stirring at
0 ºC for 1.5 h. Then material 1 (110 mg) was added to the flask,
and the resulting mixture was heated to 210 ºC for 29 h. The
(
9

6
Tetrahedron
ACCEPTED MANUSCRIPT
2
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