Glass wool: a novel support for heterogeneous catalysis

Article abstract of DOI:10.1039/c8sc02115e

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material-glass wool-can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp³-Csp³ couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp² couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.

Full text of DOI:10.1039/c8sc02115e

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Glass wool: a novel support for heterogeneous catalysis
Ayda Elhage, Bowen Wang, Nancy Marina, M. Luisa Marin†, Menandro Cruz, Anabel E. Lanterna*
and Juan C. Scaiano*
Received 00th January 20xx,
Accepted 00th January 20xx
Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease separation and reuse of
the catalyst. Here we show that a very inexpensive, manageable and widely available material – glass wool – can act as
catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu,
Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical
organic reactions including reductive de-halogenation of aryl halides, reductions of nitrobenzene, Csp3-Csp3 couplings, N-C
heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as catalyst
support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical
heterogeneous catalysts with excellent potential for flow photo-chemistry application.
DOI: 10.1039/x0xx00000x
www.rsc.org/
possibility of using fibrous materials as catalyst supports, as
they would be easy to separate after batch reactions and have
the potential for flow chemistry applications where a static
Introduction
Heterogeneous catalytic processes have several advantages
over the equivalent homogeneous ones, specifically, easy
catalyst separation, minimal product contamination1 and the
distinct possibility of reuse.2 Quite frequently these catalysts
are in the form of nanometric or micrometric powders
decorated with active nanostructures such as metal or metal
catalyst would act on flowing solutions, also facilitating
photocatalytic processes. Glass wool (GW) is inexpensive,
readily available with a variety of surface properties and easy
to modify to provide physical or chemical affinity towards
many catalytic materials. Glass wool is widely employed for
thermal and noise insulation in homes, appliances and
instrumentation. In chemistry, GW is commonly used as filter,
packing material in GC columns, purge traps and adsorbent
beds,8 where its normally regarded as a fairly robust inert
material towards many chemicals, including good pH
tolerance. There are some examples where GW is used as an
4
oxides.3, Although they are easy to separate after batch
reactions, they may not be ideal for flow chemistry, a strategy
that enables easy scale up of reactions.5 In catalysis, the term
support is used with a wide range of meanings, from the
passive support that simply restricts the mobility of the active
catalyst, to cases where the support is an integral part of the
catalyst and its performance; frequently, this is the case with
attachment surface for applications in biology, including
10
6,
7
bactericidal studies,9,
but its applications in organic
semiconductors such as TiO2.4,
Further, in the case of
chemistry are virtually unexplored. The use of glass fibers and
cloths for catalysis was reviewed in 2002;11 their applications
at the time dealt with gas and liquid processes, mostly
oxidations, but interestingly recognized that these materials
could avoid the technological problems and limitations
associated with handling and separation of powders. While
this contribution was in preparation, Barelko et al.12 published
a review with the significant technological advances achieved
during the last 15 years. Yet, with the exception of a nitro-
compound reduction, no applications to organic chemistry
were reported, in particular, not a single example on C-C bond
formation, a key reaction in organic synthesis and drug-
development applications. Some concerns about the inert
nature of the glass wool were noted many years ago by Hayes
and Macdonald, but no further studies were found in the
literature.13 Apart from these limited examples in catalysis,
where high temperature14 or redox harsh conditions are
usually employed,12 is hard to find GW uses other than the
photocatalysis the absorption and scattering properties of the
support are also important. With this in mind, we explored the
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ones mentioned above,8 largely excluding organic catalysis. shows better reactivity (vide infra). Figure 2 shows the
View Article Online
DOI: 10.1039/C8SC02115E
There are few studies focused on depositing metals on glass, materials before and after different surface modifications.
mostly dedicated to redox reactions,15-17 however to the best
of our knowledge, no complex organic reactions – such as C-C
couplings – have been explored utilizing glass as catalyst
support.
In this contribution, we report on a number of metal and metal
oxide nanostructures supported on commercially available –
sometimes modified – GW and how they perform on a variety
a
d
g
b
e
h
c
f
i
of catalytic processes. We explored individual reactions
emphasizing the use of classic reactions with diverse novel
materials. Our work on glass wool was initiated with the
assumption that this support would be of the passive type.
Notice that the use of these materials extremely facilitates the
catalyst separation from the reaction vessel, thus a regular pair
of tweezers can be used to remove the GW as shown in Figure
1. Further purification by filtration is straightforward.
Figure 2. Pictures of different materials used in this work: a) pristine SGW, b)
pristine NGW, c) HCl-treated SGW, d) APTES-functionalized NGW (NGW*), e)
Pd@SGW, f) Cu@NGW, g) Co@SGW, h) Ru@NGW* and i) Au@NGW*.
The microscopic analysis of the GW samples was also
performed. As shown in Figure 3a, the commercial GW is
constituted by glass fibers of about 10 µm diameter. The
crystalline structures present together with the fibers
correspond to NaCl as determined by a careful EDS analysis of
different areas of the image (Figure 3b,c). Upon derivatization,
the presence of metal or metal oxides nanoparticles can easily
be distinguished by SEM. Figure 3d,e show the surface of a
glass fiber covered by CoxOy NPs and the corresponding EDS
spectra. The same characterization was performed for each of
the different metal-derivatized GWs as shown in Figures S4-S7.
Figure 1. Picture showing the reaction setup used under LED irradiation and
continuous stirring (left), and the easy removal of the GW material from the
reaction vessel utilizing a pair of tweezers (right).
Results and discussion
Materials characterization
a
d
Two different types of commercial glass wool were used in this
work: non-silanized (NGW) and silanized (SGW) glass wool.
They were decorated with different metal and metal oxide
nanoparticles, namely Au, Pd, Ru, Co and Cu, utilizing
photoinduced and chemical methods as described in the SI.
The optimal synthetic method was chosen based on the
observed catalytic activity and stability of the new materials
prepared. Thus, GWs were subjected to different pre-
treatments before incorporating the metal/metal oxide
nanoparticles in order to efficiently attach the metal to the
GW surface. The experimental section summarizes several
different trials and the rationale behind the selection of the
preferred pre-treatment method. In particular, APTES
treatment was selected to add a source of amino groups on
the glass surface. These groups not only help to attach metal
nanoparticles to the glass surface but can also be used as
reducing agents for in-situ formation of metal nanoparticles
under dark conditions (See SI).18 In general, non-silanized and
silanized GW show no difference in their catalytic activity. In
particular, NGW is preferred in cases were modification with
APTES is required. When only acid pre-treatment is used, SGW
Spectrum A
e
b
c
Spectrum B
Figure 3. SEM images (top) and EDS spectra (bottom) at the marked areas of untreated
SGW (a, b, c) and of Co@SGW (d, e). Notice the particulates on the SGW fiber are
mostly composed of NaCl. Agglomerated particles were not considered to determine
particle size distribution.
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The materials were further characterized by ICP-OES, diffuse
reflectance (DR) and X-ray photoelectron spectroscopy (XPS).
The amount of metal loaded on each material as well as
particle size distribution and calculated surface area are
reported in Table 1. Figure 4 left shows the absorption profile
of SGW before and after Co-derivatization, where slight
changes on the absorption of Co@SGW can account for the
contribution of CoxOy species in the material. The different
View Article Online
DOI: 10.1039/C8SC02115E
absorption profiles of other metal-derivatized GWs are Figure 4. Left: Diffuse reflectance spectrum of HCl-treated SGW (black) and
Co@SGW (blue). Right: Deconvoluted Co 2p HR-XPS spectrum for Co@SGW
catalyst.
presented in figures S8-S11, where Pd, Au and Ru-derivatized
GW show higher absorption in the visible region compared to
the non-derivatized GW. XPS deconvolution analyses were
performed for each material in order to determine the
Catalytic activity
oxidation state of each metal. Figure 4 right shows the
deconvoluted Co 2p HR-XPS spectrum obtained for Co@SGW,
whereas the rest of the materials are described in Figures S12-
S15. Characteristic peaks for Co 2p were fitted using the spin-
orbit split constituted by Co 2p3/2 (781.2 eV) and Co 2p1/2
(797.7 eV) separated by ~16.5 eV. The corresponding Co (II)
satellites (787.4 and 803.5 eV) further proves the presence of
Co oxides (CoxOy).19 XPS analysis of the Pd@NGW* exposes a
Pd 3d core-level spectrum deconvoluted by using two spin-
orbit split Pd 3d5/2 and Pd 3d3/2 components centered at 337
eV and 342.4 eV and separated by ~5.4 eV; which more likely
corresponds to PdO.4 In contrast, more reduced Pd species are
found in the Pd@SGW material with spin-orbit components at
335 eV and 340.4 eV. The XPS fitting for the Ru 3p in Ru@NGW
reveals the presence of two main peaks at 463.1 and 485.5 eV,
which according to literature correspond to RuO2,20 although
other reports suggest a mixture between metallic Ru(0), RuO2
and RuO2•xH2O.21, 22 In the case of Cu@NGW, the two spin-
In order to determine if these new materials would perform as
catalyst we selected different reactions based on some of our
previous reports.4, 6, 7, 25 Scheme 1 summarized the reactions
tested that were successfully catalyzed utilizing the various
new materials.
A) Reductive de-halogenation of aryl halides
X
Pd or Co
X=I, Br, Cl > 99%
CH3OH, Ar, 368 nm
CO2CH3
CO2CH3
B) Reduction of nitrobenzene: to aniline
Ru, Reflux
NO2
NH2
Up to 71%
B') Reduction of nitrobenzene: to azo compounds
NH2NH2, EtOH, Air
Au, 532 nm
N
NO2
N
i-Propanol, KOH, Ar
Up to 72%
orbit split Cu 2p3/2 (934.0 eV) and Cu 2p (953.7 eV)
½
C) C-C coupling (sp3-sp3): dimerization of benzyl bromides
components (Δ~19.7 eV) and the noticeable Cu(II) satellites
indicate that CuO23 is present on this material. Finally, for
Au@NGW* the peaks corresponding to Au 4f7/2 (84.5 eV) and
Au 4f5/2 (88.0 eV) suggest the presence of Au(0). The additional
features at lower BE(~ 82 eV) can account for low-coordinated
atoms on the Au surface.24
NO2
Br
Au, 532 nm
O2N
CH2Cl2, DIPEA, Ar
O2N
Up to 80%
D) N-C heterocycloaddition: copper(I)-catalyzed azide alkyne cycloaddition
N
N
Cu, 465 nm
Table 1. Characterization of the metal content on the metal-derivatized GWs.
N3
N
+
TEA, THF, Air
Up to 95%
Materiala
Metal amount Particle size Surface area
(wt %)b
0.16 ± 0.03
0.54 ± 0.05
0.070 ± 0.005
0.030 ± 0.001
1.1 ± 0.2
(nm)c
19 ± 8
(cm2g-1)d
425
E) C-C coupling (sp-sp2): Sonogashira coupling
Pd@SGW
Pd@NGW*
Co@SGW
Ru@NGW*
Cu@NGW*
Au@NGW*
I
Pd, 465 nm
+
22 ± 9
1184
53
23
K2CO3, CH3OH, Ar
Up to 90%
89 ± 40
63 ± 30
100 ± 60
23 ± 10
Scheme 1. Scope of reactions tested with the modified glass wool composites.
Only the reactions that were successfully catalyzed are listed here.
737
0.9 ± 0.2
1215
Conditions explored for each reaction vary from thermal
control to photo-induced catalysis. Table 2 shows a summary
of the reactivity of different GW-based materials toward
different organic transformation, where the last column shows
the Table number and detailed entry for relevant examples. To
discuss their activity we divided the following sections
according to the organic transformation under study.
b
aAPTES treated GW are denoted with *. By ICP-OES analysis. None of the
metals mentioned were detected on NGW*, pristine NGW or pristine SGW.
cParticle size distributions were calculated without considering agglomerated
particles. dMetal surface per gram of glass wool; considering the mean diameter
of the GW fibers used is 10 µm, GW (d=2.2 g cm-3) surface area is approximated
to 1820 cm2g-1.
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Table 2. Summary of the best reactivities observed when various GW-based materials
are used as catalysts for different organic transformations
Table 3. Light induced reductive dehalogenation catalysed by Co- and Pd-
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DOI: 10.1039/C8SC02115E
derivatized SGW.
X
%
Yield
Table
(entry)
3 (i, vii,
xi)
3 (iv,
viii, xii)
4 (ii, iv)
Catalyst
Entry
Materiala
Co@SGW
Pd@SGW
Reaction
H3CO2C
CO2CH3
CH3OH, Ar, 368 nm
X (1)a
Catalyst
Time (h)
% Yieldb
i
>99
>99
71
A) Reductive de-
halogenation
i
ii
iii
ix
v
vi
vii
viii
Br-
Br-
Br-
Br-
Cl-
Cl-
Cl-
Cl-
Co@SGW
Pd@SGW
SGW
2
2
5
5
3
20
24
24
>99
>99
>99
98
>99
>99
37
ii
Ru@SGW*
(NGW*)
B) Reduction of
nitrobenzene to aniline
B’) Reduction of
nitrobenzene to
azobenzene
iii
none
5 (ii)
Co@SGW
Pd@SGW
SGW
iv
Au@NGW*
72
C) C-C coupling (sp3-sp3)
D) N-C
heterocycloaddition
E) C-C coupling (sp-sp2)
(Sonogashira)
80
94
6 (ii)
7 (i)
none
36
v
Au@NGW*
Cu@NGW
(NGW*)
Pd@NGW*
(SGW*)
Reaction conditions: 0.2 mmol of substrate 1, 0.36 mmol of K2CO3, 5 mL
vi
a
methanol, 60 mg catalyst under Ar. When X=I, yield of 99% is reached in
the presence of Co@SGW (or SGW) in 15 min of irradiation under Ar or 1 h
under air. Only 15 % yield detected after 24 h of reaction in the dark at 47
ºC. bYields were determined by GC-FID using t-stilbene as external
standard.
8 (i)
vii
90
a The star (*) indicates APTES-treated materials
Reductive de-halogenation of aryl halides
Reduction of nitro compounds
De-halogenation processes are usually dictated by the C-
halogen bond strength; thus, C−Cl bonds are harder to break
than C-Br bonds and those than C-I bonds, which is usually
reflected in harsher reaction conditions to achieve de-
halogenation.26, 27 Recent reports on dehalogenation processes
involved the use of either high pressure conditions (H2, 30
bar),28 or toxic and expensive iridium complexes.29 Here we
The photoreduction of nitrocompounds has been studied as a
method to synthesize anilines derivatives under mild
conditions.34, 35 Based on our previous work18 we decided to
test the ability of Ru- and Au-derivatized GW as catalysts for
the reduction of nitrobenzene to produce aniline. We used the
optimized conditions previously reported for this type of
organic transformation18, 36 (see experimental section). Table 4
summarizes the results of the nitrobenzene reduction by Ru-
derivatized GWs. We noticed that using NGW* or SGW* as
supports show no difference in the catalytic performance of
the Ru catalyst. It is worth mentioning that Au-derivatized GW
showed no catalytic activity under the same experimental
conditions. The reaction kinetics are depicted in Figure S3.
performed
photodehalogenation
of
methyl
4-
halogenobenzoates catalyzed by GW-based materials,
particularly, Pd@SGW, Co@SGW and SGW. Both Pd- and Co-
based NP are known to work as photocatalyst under UV-visible
light.30-33
Results summarized in Table 3 show the reaction in the
presence of Co@SGW proceeds under irradiation (cf. entries i
and ii) and can be accelerated under an inert atmosphere (cf.
entries i and iii). Pd@SGW and SGW show the same reactivity
as Co@SGW when methyl 4-iodobenzoate is used (entries i, iv-
v). As expected, the reaction slows down moving from iodide
to bromide and to chloride reagents (entries vii-xiv). This
tendency is more evident with catalysts as Pd@SGW and SGW,
whereas Co@SGW have shown exceptional yields, being able
to reduce methyl 4-chlorobenzoate within 3 h (entry xi, see SI
for kinetic analysis). Additionally, Co@SGW showed great
reusability; thus, after 3 catalytic cycles >99 % yield of
reductive compound was achieved within 4 h of irradiation of
methyl 4-chlorobenzoate (table S1).
Table 4. Reduction of nitrobenzene to aniline catalysed by Ru-derivatized GW.
Catalyst
NO2
NH2
NH2NH2, EtOH, Reflux, Air
Catalyst
Time (h)
% Yielda
i
ii
iii
iv
v
Ru@SGW*
Ru@SGW*
Ru@NGW*
Ru@NGW*
NGW*
24
64
24
64
24
24
28
71b
28
66c
ND
ND
vi
none
Reaction conditions: 25 mg of catalyst, 1.5 mmol nitrobenzene, 6 eq hydrazine, 5
mL ethanol. aYields were determined by GC-FID using 1,3,5-trimethoxybenzene as
an internal standard. bAfter 4 days 85% of desired product was detected. cAfter 4
days 79% of desired product was detected.
The formation of azo compounds as products of this reaction is
also possible. However, their formation under illumination is
rarely found as the reductive environment forces the reaction
toward the corresponding amine.37 There are just a few
examples where the azo-compounds forms under illumination
38, 39
of AuNP.36,
Here we show that excitation of AuNPs
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deposited on GW can also catalyze this reaction under green
light irradiation for 24 h with moderate yields (Table 5). Briefly,
the catalyst was mixed together with the nitrocompound in i-
propanol under inert atmosphere (Ar) in the presence of KOH
and irradiated with 532 nm LEDs. The formation of the
azocompound was monitored by UV-Vis spectroscopy (Figure
S4) following the azobenzene absorption band at ~350 nm. As
expected when visible light is utilized only trans azobenzene is
detected as reaction product.40
Table 6. Light induced reductive dimerization of p-nitrobenzyl bromide catalyzed by
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DOI: 10.1039/C8SC02115E
Au@NGW*.
NO2
Br
Au@NGW, 532 nm
CH2Cl2, DIPEA, Ar
O2N
O2N
Catalyst
Time (h)
% Conva
% Yieldb
i
Au@NGW*
Au@NGW*
Au@NGW*c
NGW*
5
7
77
100
ND
36
-
64
80
ii
iii
iv
v
48
24
5
ND
26
Table 5. Light induced reduction of nitrobenzene to azobenzene catalyzed by
Au@NGW*.
noned
25
vi
noned
5
-
ND
Au@NGW, 532 nm
N
NO2
N
i-Propanol, KOH, Ar
Reaction conditions: 0.1 mmol of substrate, 2 eq. of DIPEA, 30 mg of catalyst in 4
mL of CH2Cl2. aBy-product: 4-nitrotoluene. bYields and conversions were
calculated by 1H-NMR using caffeine as external standard. c Dark reaction at 39°C.
d From reference.6
Catalyst
Time (h)
% Conva
% Yielda
i
ii
iii
iv
v
Au@NGW*
Au@NGW*
Au@NGW*b
Au@NGW*c
NGW*
24
48
24
24
24
24
68
73
40
ND
ND
ND
65
72
35
ND
ND
ND
N-C heterocycloaddition (Click reaction)
We have recently reported on the photocatalyzed click
reaction using supported CuxO nanoparticles on TiO2 and
Nb2O5.7 The reaction can proceed within 6 h under both UV
and visible light. The unexpected reactivity of the material
under visible light suggests that the CuxO particles play an
important light harvesting role. With this in mind, we decided
to test the CuxO activity when deposited on GW. The efficiency
of the catalyst was compared to the reactivity of a commercial
Cu@charcoal catalyst, which is one of the preferred catalysts
to perform click chemistry under thermal conditions. As seen
in Table 7, the new material showed great reactivity and high
efficiency under both visible light irradiation or dark conditions
at 55°C (same temperature as reached upon illumination).
Unfortunately, the catalyst showed poor reusability, probably
due to the visible leaching of copper species into the solution.
vi
none
Reaction conditions: 0.3 mmol of substrate, 0.03 mmol of KOH, 5 mL i-
propanol, 60 mg catalyst under Ar. aConversion and yields were determined
by UV-vis spectroscopy. bUnder dark at 85ºC.cUnder Air.
Combining the data presented in Tables 3 and 4 it becomes
clear that GW-based catalysts offer an excellent opportunity of
product and selectivity control by tuning the metal, its loading
and the type of activation used (i.e. thermal or photochemical
activation).
C-C coupling (sp3-sp3)
The reductive dimerization of benzyl bromides can be
photoinduced using supported AuNPs and green light
excitation.6 This reaction is known as a radical reaction in
which light intensity can lead the selectivity towards the dimer
product, thus, higher intensity yields more dimer. Much to our
surprise the same reaction proceeds with excellent yields if
AuNPs are deposited on GW (Table 6). It is worthy to highlight
that a noticeable product yield is obtained in the absence of
catalyst under these irradiation conditions. These have been
Table 7. Heterogeneous photocatalytic click chemistry catalyzed by Cu@NGW.
N
N
Cu@NGW, 465 nm
N3
N
+
TEA, THF, Air
Up to 95%
Catalyst
Condition
Time (h)
% Yielda,b
previously reported as
a
contribution from the UV
contamination on the green light source.6 The material also
shows reasonable reusability (See Table S1).
i
ii
Cu@NGW
Cu@NGW
Cu@NGW
Cu@NGW
Cu@Charcoal
Cu@Charcoal
NGW
465 nm, 55 °C
Dark, 55 °C
Dark, RT
6
6
6
24
6
24
6
92 (95)
93 (94)
8 (25)
75
21
73
iii
iv
iv
iv
v
Dark, RT
Dark, 55°C
Dark, 55°C
Dark, 55°C
Dark, 55°C
ND
vi
NGW
24
2c
Reactions conditions: 15 mg of catalyst, azide/alkyne/TEA (1:1:1), 6 h under air.
aYields were calculated by 1H-NMR analysis in CDCl3 using caffeine as external
standard. bValues between brackets are yields obtained after 6 h of reaction
using supported Cu@NGW*. cMixture of two isomers
C-C coupling (sp-sp2) (Sonogashira)
One of our recent reports demonstrated that PdNP-decorated
materials such as TiO2, nanodiamonds and Nb2O5 can
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selectively catalyze the cross-coupling of iodobenzene and
phenylacetelyne under both reflux and visible light
irradiation.32 Here we show that the same reaction can be
catalyzed by the new Pd@SGW* and Pd@NGW* catalysts and
selectively lead to the cross-coupling products showing similar
activity. Briefly, the selective cross coupling reaction of
iodobenzene and phenylacetylene has been studied in
methanol as solvent, K2CO3 as base and supported PdNPs on
activated and/or functionalized surface of GW (Table 8).
Control reactions in the presence of GW and in the absence of
catalyst did not show any product after 24 h. The
photocatalyst can be reused at least two times with excellent
performance (See Table S1), showing the same reactivity as
the previous reported materials.32
Experimental
General
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DOI: 10.1039/C8SC02115E
Unless otherwise specified, all chemicals were purchased from
Sigma-Aldrich or Fisher Scientific and used without further
purification. Particularly, the following glass wools were used:
Non-treated GW (Aldrich catalog #: 20384) and silanized GW
(Aldrich catalog #: 20411). Irgacure-2959 (I-2959) was
purchase from Ciba.
Scanning electron microscopy (SEM) images were carried out
in a JEOL JSM-1600 SE microscope working at an accelerating
voltage of 2 kV. X-ray photoelectron spectroscopy (XPS) was
recorded using Kratos analytical model Axis Ultra DLD, using
monochromatic aluminum Ka X-rays at 140 W. XPS data was
analyzed using CasaXPS software, Version 2.3.15. All spectra
were calibrated at the C 1s signal at 284.8 eV and fittings
obtained using a Gaussian 30% Laurentian and a Shirley
baseline. The amount of metal loaded onto the materials was
determined by Inductively Coupled Plasma Optical Emission
Spectrometry (ICP-OES), using an Agilent Vista Pro ICP
Emission Spectrometer. Approximately 10 mg portions were
accurately weighed in triplicate and digested with aqua regia.
Solutions were further diluted and measured by ICP-OES. The
following emission lines were used for quantification when
applicable: Pd 229.65 nm, Au 267.59 nm, Cu 327.00 nm, Co
228.00 nm, Ru 245.55 nm. Diffuse reflectance measurements
were carried out in Agilent Cary 7000 UV-Vis-NIR Universal
Measurement Spectrophotometer coupled with an Agilent
praying Mantis accessory. UV-Vis spectroscopy was carried out
in an Agilent Cary 60 UV-Vis Spectrophotometer.
Table 8: Light-induced Sonogashira C-C coupling catalyzed by Pd@GW.
I
Pd@NGW, 465 nm
K2CO3, CH3OH, Ar
+
Up to 89%
Catalyst
Time (h)
% Conv
% Yielda
i
Pd@NGW*
Pd@NGW*
NGW*
5
5
24
24
>99(>99)
90 (88)
ND
ND
iib
ii
0
0
0
iv
none
ND
Reactions conditions: 1 eq. of Iodobenzene, 1.3 eq. of Phenylacetylene, 2 eq. of
K2CO3, 4 mL methanol, 60 mg Pd@NGW*. aYields were determined by GC-FID
using t-butylbenzene as an external standard. bUnder dark conditions, reaction
was run at 42 °C. Values between brackets are yields obtained after 5 h of
reaction using supported Pd@SGW*.
UV irradiation used for catalyst synthesis was performed in a
Luzchem photoreactor equipped with UVA bulbs (typically
operated with 14 bulbs, corresponding to ~0.029 W/cm2 (with
~ 4% spectral contamination). Light-emitting diodes (LEDs) of
10 W from LedEngin were used for photocatalytic reactions in
the visible region (centered at 465 and 532 nm, respectively)
and in the UV region (centered at 368 nm), Figure S1.
Conclusions
We show the versatility of the use of glass wool as a very
inexpensive, widely available and easy handled material for
heterogeneous catalysis. We demonstrate that despite the
different nature of the glass wool utilized, the efficacies of at
least two commercial materials are similar. We have explored
different methods to activate the glass surface in order to
better anchor the catalytic species to the material. Also, low
surface loadings (ranging from 1 down to 0.07 wt%) with
different types of metal or metal oxide nanoparticles were
tested, to illustrate how easy to use and reliable these
materials are. The materials excel in both thermal and light-
Quantification was carried out in a Perkin Elmer, Claurus Gas
Chromatograph coupled to a Flame Ionization Detector (FID)
and using a DB-5 column (30 m length, 0.320 mm diameter,
0.25 μm film), Helium as a carrier gas and t-butyl benzene as
external standard. GC-MS analyses were performed on an
Agilent 6890-N Gas Chromatograph with an Agilent 5973 mass
1
selective detector calibrated with acetophenone. All H NMR
spectra were recorded on a Bruker AVANCE 400 spectrometer
expressing the chemical shifts in ppm relative to the H-signal
of tetramethylsilane (TMS).
induced catalysis in
a
variety of different organic
transformations ranging from reductions to C-C couplings and
cyclizations, showing adaptability to different reaction media
and conditions. Also important, the material can be easily
separated from the reaction mixture eliminating tedious
workup. Notice that optimization of the metal loadings could
indeed open the door for more exploratory studies of these
materials. This is a first effort on the use of GW as a catalytic
support for fine organic reactions and more complex and
interesting systems can be developed from here. We envision
Catalyst Preparation
Glass wool pre-treatments
Two types of glass wool were used for this work: silanized glass
wool (SGW) and non-silanized glass wool (NGW). The materials
were used as received or treated by different methods
described in the SI.
this as
a first step towards an easy way to recover
Metal decoration
heterogeneous catalysts, and to develop catalysts with great
flow chemistry potential.
Metal or metal oxide nanoparticles were grafted on activated
GW surface using different thermal and photochemical
6 | J. Name., 2012, 00, 1-3
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methods. The photochemical method is based on a previously Thermal-induced isomerization:
View Article Online
described protocol41 to synthesize metal NP utilizing Irgacure 50 mg of Ru@NGW* (or Ru@SGW*) were dispersed in 8 mL of
2959 (I-2959) as photoinitiator. I-2959 can undergo Norrish i-propanol by sonication ca. for 5 min in a clean round bottom
DOI: 10.1039/C8SC02115E
Type
I cleavage upon UVA excitation, generating the flask, then 25 μL (0.16 mmol) of reactant were added. The
corresponding acetyl and ketyl radicals. The latter have been reaction mixture was heated up to 85 ºC (solvent boiling point)
described as strong reducing agents capable of reducing under air with continuous stirring for 24 hours. The progress of
different metals cations (Mn+) into the resultant metal (M0) as the reaction was monitored by GC-FID. The solid catalyst was
shown in scheme S1. In general, 500 mg of activated GW (SGW separated by filtration and crude product was obtained after
or NGW) and the corresponding amount of metal precursor solvent evaporation. Quantification was done by GC-FID.
were mixed together in 200 mL of Milli-Q water and sonicated. Light-induced isomerization or hydrogenation:
10 mL of ethanolic solution of I-2959 are added and irradiated 60 mg of Pd@NGW*(or Pd@SGW) were dispersed in 4 mL of
under UVA for ~1h. Detailed synthetic methodologies are methanol in a clean glass tube, then 0.14 mmol of estragol
described in the SI.
were added. The reaction mixture was purged with argon for
Although some metals are in the form of metal oxides upon 15 min then irradiated with 465 nm LED (368 nm LED for
deposition on the GW surface, we will refer to all materials as hydrogenation) for 24 hours at room temperature. The
M@GW. In many cases metal oxide nanoparticles are formed progress of the reaction was monitored by GC-FID. The solid
spontaneously following ambient exposure of metal catalyst was separated by filtration, crude product was
nanoparticles.
Catalytic reactions
obtained after solvent evaporation. Quantification was done
either by 1H-NMR or by GC-FID.
Unfortunately, no reaction was detected under neither of
these conditions.
Reductive dehalogenation
60 mg of catalyst (Co@SGW, Pd@SGW or SGW) were
dispersed in 5 mL of methanol in a clean quartz tube, then 0.2
mmol of methyl 4-halobenzoate and 0.36 mmol of K2CO3 were
added. The reaction mixture was purged with Ar for 10 min
then irradiated with 368 nm LED light source working at 0.4
Wcm-2. The solid catalyst was separated by filtration.
Quantification of the product was done by GC-FID using t-
stilbene as external standard. Time of irradiation varies
depending on the aryl halides.
C-C coupling (sp-sp2)
Thermal-induced Sonogashira C-C coupling:
60 mg of Pd@NGW* (Pd@SGW or Ru@NGW) were dispersed
in 4 mL of methanol by sonication for about 5 min in a clean
round bottom flask. Then 0.12 mmol of iodobenzene, 0.16
mmol of phenylacetylene and 0.24 mmol of K2CO3 were added.
The reaction mixture was purged with Ar and heated up to 42
°C (temperature of reaction mixture under blue LED
irradiation) with continuous stirring for 5 hours. The solid
catalyst was separated by filtration and crude product was
obtained after solvent evaporation. Quantification was done
by GC-FID.
Nitrobenzene reductions
Aniline formation:
Using Ru@NGW* or Ru@SGW*. 25 mg of catalyst were placed
in a centrifuged tube together with 1.5 mL of nitrobenzene (1
M), 1.7 mL of EtOH, 0.3 mL internal standard 1,3,5-trimethoxy
benzene (0.5M) and 1.5 mL NH2NH2 solution (6M). The tube
was tightly closed and immersed in oil bath at 78 °C under
constant stirring. Aliquots of 15 µL were taken from reaction
mixture, diluted with 1.5 mL of ethylacetate prior to GC-FID
quantification.
Using Au@NGW*. 60 mg of Au@NGW* were dispersed in 5mL
of EtOH in a clean dry round bottom flask then 1 mmol of
nitrobenzene and 5 mmol of hydrazine were added. The
resulting mixture was heated up to 78 °C under continuous
stirring. The progress of the reaction was monitored by UV-
visible spectroscopy. No reaction was detected under these
conditions.
Light-induced Sonogashira C-C coupling:
60 mg of Pd@NGW* (or Ru@NGW) were dispersed in 4 mL of
methanol in a 10 mL clean glass tube, then 0.12 mmol of
Iodobenzene, 0.16 mmol of phenylacetylene and 0.24 mmol of
K2CO3 were added. The reaction mixture was purged with Ar
for 15 min then irradiated with 465 nm LED light source set up
at 1 W/cm2 for 5 hours. The solid catalyst was separated by
filtration and crude product was obtained after solvent
evaporation. Quantification was done by GC-FID. Control
experiments were carried out as mentioned above. Notice that
no reaction was detected under these conditions when using
Ru@NGW as catalyst; only Pd@NGW* was effective.
N-C heterocycloaddition
We followed a previously reported protocol.7 Briefly, 15 mg of
Cu@NGW (or Cu@NGW*) were dispersed in 1.5 mL of THF in a
quartz test tube and mixed with the azide (0.5 mmol), alkyne
(0.5 mmol), and amine (0.5 mmol). The reaction mixture was
stirred and irradiated with 465 nm LED at room temperature
and under air for 6 h. The solid catalyst was separated by
filtration and the pure product was obtained after vacuum
evaporation. Yields calculated by 1H NMR in CDCl3.
Control experiments were performed under dark conditions at
room temperature or at 55°C (Maximum temperature reached
upon illumination) under air.
Azobenzene formation:
60 mg of Au@NGW* (or Ru@NGW) were dispersed in 5 mL of
i-propanol in a clean glass tube and then 0.03 mmol of KOH
and 0.3 mmol of nitrobenzene were added. The resulting
mixture was sonicated for 5 min prior to irradiation using a 532
nm LED. The solid catalyst was removed by filtration and
quantification was done by UV-visible spectroscopy (Figure
S4). Notice that no reaction was detected under these
conditions when Ru@NGW was tested as catalyst.
Isomerization/hydrogenation of estragol
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Journal Name
C-C coupling (sp3-sp3): dimerization of benzyl bromides
We followed a previously reported protocol.7 Briefly, 30 mg of
Au@NGW* were dispersed in 4 mL of dichloromethane DCM
in a glass test tube then 0.1 mmol of 4-nitrobenzylbromide and
0.2 mmol of diisopropyl ethylamine (DIPEA) were added. The
resulting mixture was purged with argon for 15 minutes prior
to 532 nm LED irradiation with a 4xLED system each working at
0.56 W/cm2. The solid catalyst was separated by filtration and
the product was obtained after vacuum evaporation. Yields
and conversions were calculated by 1H NMR in CDCl3 using
caffeine as external standard. Control experiments were
carried out as mentioned above.
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Catalyst Recyclability
Co@SGW, Pd@NGW* and Au@NGW* catalysts were tested
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then dried in the oven at 100 °C overnight prior to reuse (Table
S1).
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
This work was supported by the Natural Sciences and
Engineering Research Council of Canada, the Canada
Foundation for Innovation, the Canada Research Chairs
Program and funding from Canada’s International
Development Research Centre (IDRC). Thanks are due to the
RISE program for the scholarship awarded to M.C. and the
Generalitat Valenciana (BEST/2017/049) for the financial
support granted to M.L.M. The authors would like to thank Dr.
Yun Liu for helping on the acquisition of the SEM images.
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Table of Contents graphic
Easy catalyst separation
N3
+
X
I
+
De-halogenations
Reduction of nitrobenzene
C-C couplings
CO2CH3
NO2
Br
N-C couplings
O2N
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