Mild bottom-up synthesis of indium(0) nanoparticles: Characterization and application in the allylation of carbonyl compounds

Article abstract of DOI:10.1039/c5ra27928c

Very reactive, monodisperse (4.0 ± 0.5 nm) spherical indium(0) nanoparticles have been generated in situ, in a simple, mild and efficient way, by fast reduction of commercially available indium(iii) chloride with lithium sand and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB) in THF, at room temperature, and in the absence of any anti-agglomeration additives or ligands. The as-synthesized bare InNPs were applied for the allylation of a variety of aldehydes and ketones. For most of the compounds tested, the corresponding homoallylic alcohols were obtained as the major product in good to excellent yield.

Full text of DOI:10.1039/c5ra27928c

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Journal Name
ARTICLE
Mild bottom-up synthesis of indium(0) nanoparticles:
characterization and application in the allylation of carbonyl
compounds.†
Received 00th January 20xx,
Accepted 00th January 20xx
Viviana Dorn,* Alicia Chopa and Gabriel Radivoy
DOI: 10.1039/x0xx00000x
Very reactive, monodisperse (4.0±0.5 nm) spherical indium(0) nanoparticles have been generated in situ, in a simple, mild
and efficient way, by fast reduction of commercially available indium(III) chloride with lithium sand and a catalytic amount
of 4,4´-di-tert-butylbiphenyl (DTBB) in THF, at room temperature, and in the absence of any anti-agglomeration additive or
ligand. The as-synthesized bare InNPs were applied for the allylation of a variety of aldehydes and ketones. For most of the
compounds tested, the corresponding homoallylic alcohols were obtained as the major product in good to excellent yield.
www.rsc.org/
digestive ripening of indium shot)5e provide little control over
particle size and size distribution, and require the use of
specific and/or sophisticated laboratory equipment. Some of
these methodologies allow the synthesis of particles less than
10 nm in size but require very high temperatures and/or high
vacuum techniques, and the use of amine or phosphine ligands
to passivate the surface of InNPs. On the other hand, the
bottom-up methods generally involve the reduction of indium
salts by strong reducing agents at high temperatures (e.g.
sodium metal,6a sodium borohydride in ionic liquids (IL),6b by a
Introduction
The synthesis of metal nanoparticles (NPs) has attracted
significant attention in the last decades, mainly because of
their exceptional size-dependent physical and chemical
properties.1 In this sense, while the specific role of metal NPs
as catalysts in diverse chemical reactions is not trivial, their
unique catalytic properties are strongly related to the high
surface area and the possibility of charge distribution in
electron transfer reactions.2 Besides, the catalytic activity of
many metal NPs is commonly affected by the method of
preparation and also by the source of the metal, the reaction
conditions, and the use of additives such as stabilizing agents.3
Even though the first scientific work on the use of indium
metal in synthetic organic chemistry was reported in 1975,4a in
the last years the application of indium metal particles in
organic synthesis has gained relevance, being widely used as
catalysts in a variety of organic transformations.4b-e This
renaissance of indium chemistry could be explained taking into
account that indium-based reagents are stable to air and
moisture, minimally toxic to human health and the
environment, highly selective, and compatible with many
functional groups. In spite of this, the synthesis of indium
nanoparticles (InNPs) has been scarcely reported. Regrettably,
most of the top-down methods (e.g. dispersion of bulk indium
in paraffin oil,5a ultrasound irradiation,5b thermal evaporation
combined with aerosol technology,5c sputter deposition of
indium foil,5d solvated metal atom dispersion followed by
two-step phase-transfer reaction in the presence of
a
surfactant).6c Most of these methods produce particles with
average sizes in the range of 10-100 nm in diameter. Recently,
InNPs less than 10 nm were prepared via reduction of indium
salts with different reducing systems; among them, lithium
borohydride in amine solvents,7a electrochemical reduction in
IL7b or by
thermal decomposition of organometallic
complexes.7c It is noteworthy that with all of these
methodologies it is mandatory the use of stabilizing agents to
prevent particle agglomeration.
On the other hand, the use of alkali-metals in combination
with arenes as electron carriers, are well known as highly
efficient reducing systems. In the last decade, some of us have
been working on the preparation of transition metal NPs by
fast reduction of commercially available metal chlorides with
lithium sand and a catalytic amount of an arene [naphthalene,
4,4´-di-tert-butylbiphenyl (DTBB)] as electron carrier in
tetrahydrofuran (THF) as the solvent and at room
temperature. This methodology allowed the preparation of
very reactive, monodisperse spherical nickel, iron, copper,
manganese, cobalt and titanium nanoparticles with an average
size near 3.5±1.5 nm. These metal nanoparticles, either
unsupported or supported over different materials, efficiently
catalyzed a wide variety of useful synthetic transformations,
mainly reduction8 and coupling reactions.9
Instituto de Química del Sur, INQUISUR (CONICET-UNS), Departamento de Química,
Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahía Blanca, Argentina.
†In honour of Prof. Bruno Vuano.
*vdorn@uns.edu.ar
Electronic Supplementary Information (ESI) available: Detailed experimental
procedures, characterization data, and full characterization of InNPs are included.
See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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Metal-mediated allylation of carbonyl compounds is a broadly The UV absorption spectrum of InNPs showed a characteristic
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DOI: 10.1039/C5RA27928C
used synthetic tool that allows the construction of new C˗C band at 260 nm, attributed to the surface plasmon resonance
bonds, giving rise to homoallylic alcohols10 which are of indium nanoparticles, and was obtained after evaporating
important building blocks in organic synthesis. In this regard, the THF (20 mbar) and re-dispersing the nanoparticles in
since the first work reported by Butsugan et al. in 1988,11 the dichloromethane (DCM).
indium-mediated
allylation
reaction
has
developed Data obtained from the X-ray diffraction (XRD) and the X-ray
exponentially over the past decades,12 nevertheless, there is photoelectron spectroscopy (XPS) analysis of the InNPs, were
only one paper in the scientific literature about the use of matched with those reported5b and confirmed the presence of
InNPs (ca. 100 nm) for the allylation of carbonyl compounds. indium (see ESI for experimental details and characterization
These indium nanoparticles were synthesized from bulk of the InNPs).
indium metal and required high temperatures and long
reaction times.13
Allylation of carbonyl compounds promoted by InNPs
Herein, we report a one-pot, simple, mild and efficient
As it was mentioned, the InNPs were in situ generated and we
synthesis of very reactive, monodisperse (4.0±0.5 nm)
choose benzaldehyde as model substrate to optimize the
spherical indium(0) nanoparticles, by fast reduction of
stoichiometry and reaction time for the allylation reaction.
indium(III) chloride with lithium sand and a catalytic amount of
The best results were obtained by using InCl3 (1.0 mmol) with
4,4´-di-tert-butylbiphenyl (DTBB) in THF at room temperature,
an excess of lithium sand (3.5 mmol) in the presence of DTBB
and in the absence of any anti-agglomeration additive or
(0.1 mmol) as electron carrier, THF (2 mL) as the solvent, with
ligand. The InNPs were morphologically and physicochemically
allyl bromide (1.5 mmol dissolved in
1 ml THF) and
characterized by means of different techniques. The as-
synthesized bare InNPs were applied for the allylation of a
variety of aldehydes and ketones. For most of the compounds
tested, the corresponding homoallylic alcohols were obtained
in good to excellent yields without observing the presence of
byproducts such as alcohols (reduction) or pinacols (reductive
coupling). To the best of our knowledge, this is the first report
describing the synthesis and application of unsupported InNPs
in a one-pot organic transformation under mild reaction
conditions.
benzaldehyde (0.5 mmol dissolved in 1 ml THF) at room
temperature and under a nitrogen atmosphere. The use of a
half amount of InCl3 (0.5 mmol), notably reduced the yield of
the homoallylic alcohol 2a (98% to 56%) (Table 1, compare
entries 1 and 2).
Table 1. Indium mediated allylation of carbonyl compounds
with allyl bromide.
Results and discussion
Synthesis and characterization of InNPs
Carbonyl
compound 1
Reaction time (h)
Yield 2 (%)c
R1
R2
H
InNPsa In powderb
InNPs
98
In powder
82d,e
The indium nanoparticles were generated by fast reduction of
commercially available InCl3 with an excess of lithium sand
(1:3.5 ratio relative to the corresponding indium trichloride),
and a catalytic amount of DTBB (10 mol% referred to the
indium salt), in THF as the solvent, at room temperature and
under a nitrogen atmosphere. Typical transmission electron
microscopy (TEM) micrograph and size distribution graphic for
InNPs are shown in Figure 1. Well defined, monodisperse
spherical nanoparticles were observed with a particle size
distribution range of ca. 4.0±0.5 nm.
1
Ph
1
3
2a
2a
2b
2c
2c
2f Ph
H
1
---
30
26
---
56
67e
76e,g
---
59e
36e
3
Ph
CH3
20
20
20
4
5h
-(CH2)5-
-(CH2)5-
96
---
a Reaction conditions: Li (3.5 mmol), DTBB (0.1 mmol), InCl3 (1.0 mmol) in
THF (2ml), allyl bromide (1.5 mmol) in THF (1 ml), stirred for 30 min,
carbonyl compound (0.5 mmol) in THF (1 mL), at 25 ºC. Reaction
b
c
performed with In powder (1.0 mmol). Determined by GC using an
d
internal standard. Together with reduced starting carbonyl compound
(10%). e Together with unreacted starting carbonyl compound. f Reaction
performed by using InCl3 (0.5 mmol). g Together with α-allylketone (9%).
h
Reaction performed by using Li (3 mmol) and stirring with the allyl
bromide for 60 min.
On the other hand, the reaction performed between allyl
bromide and benzaldehyde, in the presence of InCl3, gave no
conversion to 2a and the starting carbonyl substrate was
recovered.
Under the optimized conditions, we investigated the reaction
Figure 1. TEM micrograph and size distribution of the InNPs. of three different carbonyl compounds with allyl bromide in
The sizes were determined for 100 nanoparticles selected at
random.
the presence of the in situ generated InNPs (1 mmol) or In
powder (-325 mesh, 1 mmol), as indium metal sources.
2 | J. Name., 2012, 00, 1-3
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As can be seen in Table 1, the allylation of benzaldehyde bromide as allylating agent, the yield of the corresponding
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promoted by In powder gave 1-phenylbut-3-en-1-ol (2a, 82%) alcohol 2e (1-phenyl-3-methylbut-3-en-1-ol) was
DOI: 10.1039/C5RAn2o7t9a2b8lCy
after 3 h, together with direct reduction product (10%) and a higher when using InNPs compared to that obtained when
little amount of the starting carbonyl compound, whereas, as using indium powder (99% to 10%). Furthermore, in the latter
above mentioned, the same reaction mediated by InNPs gave reaction, a considerable amount of the starting benzaldehyde
total conversion into the corresponding alcohol 2a in a shorter was recovered at the final reaction time (2 h) (Table 2, entry
reaction time (1 h) (Table 1, entry 1). On the other hand, the 3). Prenyl bromide showed to be less reactive, so it was
allylation of acetophenone mediated by In powder led to 2- necessary to stirr the InNPs suspension with the prenyl
phenylpent-4-en-2-ol (2b) in 59% yield after 30 h, and bromide for 60 min prior to the addition of benzaldehyde.
allylation of cyclohexanone under the same conditions gave 1- Thus, after 4 h reaction time, the γ-adduct 1-phenyl-2,2-
allylcyclohexanol (2c) in only 36% yield after 26 h. dimethylbut-3-en-1-ol (2f) was obtained in 65% yield in the
Furthermore, a considerable amount of starting ketone was presence of indium powder, and in 95% yield when the
recovered at the end of the reaction in both cases (Table 1, reaction was mediated by InNPs (Table 2, entry 4). The less
entries 3 and 4). When InNPs were used as the indium source, reactivity observed for prenyl bromide could be attributed to
better yields of the corresponding homoallylic alcohols, 2b and the steric hindrance caused by methyl substituents attached to
2c, were observed. Thus, homoallylic alcohol 2b was obtained the allyl moiety, which could affect, to a some extent, the
in 67% yield after 20 h (Table 1, entry 3), and the yield of the formation of the homoallylic alcohol.
homoallylic alcohol 2c was markedly improved compared to As expected, allyl chloride showed a lower reactivity than allyl
that obtained by using indium powder (36% to 76%, Table 1, bromides, and it was necessary to stirr the suspension of InNPs
entry 4). In this last case, the formation of the corresponding and allyl chloride for 28 h before adding benzaldehyde to
α-allyl ketone as by-product was detected (Table 1, entry 4, obtain the homoallylic alcohol 2a in a 87% yield. Under the
and footnote g). We suppose that the formation of this by- same conditions, 2a was obtained in 45% yield in the presence
product might proceed through the alkylation of the ketone of indium powder (Table 2, entry 5).
enolate generated by the excess of lithium metal present in The results obtained for the different carbonyl compounds
the reaction medium. To confirm this assumption we (Table 1) and the different allyl halides tested (Table 2), show
reproduced the same allylation reaction conditions but in the that the reactions promoted by InNPs gave better yields of the
absence of the indium salt. Thus, the α-allyl ketone product corresponding homoallylic alcohol products 2, and in shorter
was obtained in ca. 40% yield together with the starting reaction times, than those mediated by indium powder,
cyclohexanone. Moreover, we assumed that an allyl indium probably as a consequence of the higher surface-to-volume
intermediate could be formed under our reaction conditions, ratio of the InNPs.
thus, in order to favor the formation of this plausible
intermediate in the absence of any excess of lithium metal, we Table 2. Indium mediated allylation of benzaldehyde with allyl
tested the allylation of cyclohexanone under the optimized halides.a
conditions but using a stoichiometric amount of lithium (3.0
mmol) and stirring the in situ generated InNPs suspension with
the allylating agent for 60 min, prior to the addition of the
carbonyl compound. As expected, under these conditions,
cyclohexanone gave the corresponding product 2c in excellent
yield (96%) (Table 1, entry 5).
Reaction
time (h)
Allyl halide 3
Yield 2 (%)b
Then, we investigated the allylation reaction of benzaldehyde
by using different allylating agents, both in the presence of in
situ generated InNPs (1 mmol) or In powder (1 mmol). The
reaction of benzaldehyde with allyl bromide, mediated by
indium powder, after 1 h, gave 1-phenylbut-3-en-1-ol (2a) in
74% yield together with the starting carbonyl compound. As
we mentioned above, the same reaction mediated by InNPs
gave the homoallylic alcohol 2a almost quantitatively (98%)
after 1 h of reaction time (Table 2, entry 1). The crotylation of
benzaldehyde mediated by indium power gave 1-phenyl-2-
methylbut-3-en-1-ol (2d) with moderated yield (58%) together
with the starting carbonyl compound, whereas in the presence
of InNPs afforded the corresponding γ-coupled homoallylic
R1
H
R2
H
R3
H
X
InNPs In powder
98
99d
74c
58c
10c
65c,e
45c,f
1
2
Br
1
2
2a
2d
H
CH3
H
Br
3
4
CH3
H
H
CH3
H
H
CH3
H
Br
Br
Cl
2
4
8
2e
2f
99
95e
87c,f
5
a
H
2a
The reaction conditions are the same of Table 1 for both indium
sources. b Determined by GC using an internal standard. Together with
c
unreacted benzaldehyde. Syn:anti, 67:33 determined by 1H NMR.
d
e
f
Reaction performed by stirring the allyl bromide for 60 min. Reaction
performed by stirring the allyl chloride for 28 h.
alcohol 2d almost quantitatively after
2
h. The
In order to assess the scope of the InNPs-mediated allylation
of carbonyl compounds (Table 3), we tested the allylation
reaction of (-)-mentone, which proceeded with very low
conversion (2g, ca. 12%) of the starting cyclic ketone after 24
diasterereoselectivity observed for this reaction (67:33
syn/anti) was slightly better than that previously reported by
other authors for bulk indium mediated crotylations,11a being
the syn-isomer dominant (Table 2, entry 2). With methallyl
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h. The lack of reactivity observed for this substrate could be ortho- and para-substituted benzaldehydes bearing either
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attributed to the steric hindrance caused by the iso-propyl electron-donating or electron-withdrawiDnOgI:g1r0o.1u0p3s9,/Cle5RdA2to792t8hCe
substituent attached to the α-position of the carbonyl group, corresponding alcohols in excellent yields and in rather short
which could make it difficult the approach of the allyl-indium reaction times. Thus, o-methoxy- and o-chlorobenzaldehyde
intermediate to the electrophilic center. Moreover, the gave 1-(2-methoxyphenyl)-3-buten-1-ol (2o) (97%, 30 min) and
allylation of 3-pentanone, a less hindered acyclic aliphatic 1-(2-chlorophenyl)but-3-en-1-ol (2p) (72%, 1 h), respectively.
ketone, resulted in a 30% yield of the homoallylic alcohol 2h Also, ortho-benzaldehydes bearing strongly electron-
after 24 h. On the other hand, aldehydes showed to be more withdrawing groups such as trifluoromethyl or nitro, gave the
reactive than ketones. Thus, the allylation of heptanal gave 1- corresponding 1-(2-(trifluoromethyl)phenyl)-3-buten-1-ol (2q)
decen-4-ol (2i) in 93% yield after 1 h, and phenylacetaldehyde, and 1-(2-nitrophenyl)-3-buten-1-ol (2r) in 99% and 95% yield (1
after 5 h, gave the homoallylic alcohol 2j (1-phenyl-4-penten- h), respectively. It should be mentioned that ortho-
2-ol) in an almost quantitative yield.
salicylaldehyde did not yield the expected homoallylic alcohol
With the aim to study the compatibility of our methodology and the starting aldehyde was recovered unreacted. We
with the presence of reducible functional groups in the starting suppose that this lack of reactivity could be due to the
carbonyl compounds, we tested the allylation of an presence of a very stable intramolecular hydrogen bond that
unsaturated aldehyde as (-)-citronellal. The reaction led to the would prevent the reaction of the carbonyl group with the allyl
alcohol product 2k (6,10-dimethylundeca-1,9-dien-4-ol) as a indium intermediate.
ca. 1:1 mixture of both possible diastereoisomers in 95% yield,
Table 4. InNPs mediated allylation of substituted
the carbon-carbon double bond remaining intact. More
interesting was the chemoselectivity to the C=O bond
observed in the allylation of the α,β-unsaturated aldehyde (E)-
2-methyl-2-butenal, which led to (E)-5-methyl-1,5-heptadien-
4-ol (2l) in 91% yield after 30 min. Other aromatic aldehydes as
furfural and 1-naphtaldehyde gave the corresponding
homoallylic alcohols 1-(2-furfuryl)-3-buten-ol (2m) and 1-(1-
naphtalenyl)-3-buten-ol (2n) in 82% and 98% yield,
respectively and in short reaction times (Table 3).
benzaldehydes with allyl bromide.a,b
Table 3. InNPs mediated allylation of carbonyl compounds
with allyl bromide.a,b
a
Reaction conditions: Li (3.5 mmol), DTBB (0.1 mmol), InCl3 (1.0 mmol)
in THF (2 mL), allyl bromide (1.5 mmol) in THF (1 mL), stirred for 30
min, carbonyl compound (0.5 mmol) in THF (1 ml), at 25 ºC, 1 h
b
reaction time. Quantified by GC analysis using internal standard
method. c Together with starting substrate.
a
Reaction conditions: Li (3.5 mmol), DTBB (0.1 mmol), InCl3 (1.0 mmol)
in THF (2 mL), allyl bromide (1.5 mmol) in THF (1 mL), stirred for 30
b
Benzaldehydes substituted in para position also shown to be
very reactive. Thus, p-methoxy- and p-methylbenzaldehyde
gave 1-(4-methoxyphenyl)-3-buten-1-ol (2s) and 1-(4-
methylphenyl)-3-buten-1-ol (2t), in 85% and 99% yield,
respectively. Moreover, p-chloro- and p-bromobenzaldehyde
gave the corresponding alcohols 2u (1-(4-chlorophenyl)-3-
min, carbonyl compound (0.5 mmol) in THF (1 ml), at 25 ºC.
c
Quantified by GC analysis using internal standard method. Together
with starting substrate.
Finally, we evaluated the compatibility of our methodology
with the presence of different substituents attached to the
aromatic ring of benzaldehyde. The results summarized in
Table 4 show that, under the optimized conditions, different
buten-1-ol)
and
2v
(1-(4-bromophenyl)-3-buten-1-ol)
respectively in 98% yield, without dehalogenation of the
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starting aldehyde. The reaction carried out with almost quantitatively and in short reaction times. Besides, the
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DOI: 10.1039/C5RA27928C
terephthaldehyde gave 1,1'-(1,4-phenylene)bis(3-buten-1-ol) methodology showed to be compatible with the presence of a
(2z) in excellent yield (93%). All our attempts for the allylation variety of functional groups in the starting carbonyl
of only one of the two carbonyl groups of this substrate by compounds. Although the exact mechanistic pathway is
controlling the stoichiometry of the reaction (adding only 0.5 difficult to ascertain, based on the experimental data
mmol of the allyl bromide) were unsuccessful. Finally, para- obtained, we think that the reaction mechanism implies the
substituted benzaldehydes bearing strongly electron- formation of γ-coupling products via a cyclic six-membered
withdrawing groups such as cyano and nitro, led to the Zimmermann-Traxler-type transition state, and the
corresponding homoallylic alcohols almost quantitatively participation of allyl indium(III) species as intermediates. To
(Table 4, 2x and 2y).
the best of our knowledge, this is the first organic functional
Although the exact structure of the allyl indium intermediates group transformation based on the use of in situ prepared
remains to be elucidated, based on the stoichiometry of the indium nanoparticles.
reaction, our experimental observations and previous reports
by other authors,14 we propose a plausible reaction pathway
Acknowledgements
for the studied transformation. As can be seen from Scheme 1,
the first step in the reaction would be the formation of InNPs
by electron transfer (SET) from the arene radical anion to the
indium salt. The addition of the allyl bromide to the InNPs
suspension, could led to the formation of an allyl indium(III)
intermediate, which by reaction with the activated carbonyl
compound (probably adsorbed to the InNPs surface) could led
to the corresponding γ-coupling homoallylic alcohol through a
Zimmerman-Traxler-type transition state.
This work was generously supported by the Consejo Nacional
de Investigaciones Científicas y Técnicas (CONICET), Agencia
Nacional de Promoción Científica y Tecnológica (ANPCyT),
Comisión de Investigaciones Científicas (CIC) and Universidad
Nacional del Sur (UNS) from Argentina. The authors also would
like to thank the Research Technical Services of Universidad de
Alicante.
Notes and references
1
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2
3
J. D. Aiken, R.G. Finke, J. Mol. Catal. A: Chem. 1999, 145, 1.
(a) P. Cintas, Activated Metals in Organic Synthesis, CRC:
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Nanoparticles: From Theory to Application, G. Schmid, Ed.,
Wiley–VCH: Weinheim, 2005, pp 185–199.
4
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Scheme 1. Proposed reaction pathway for the InNPs-mediated
allylation of carbonyl compounds.
Conclusions
We have developed a simple and convenient methodology for
the synthesis of very reactive, well defined, monodisperse,
spherical InNPs with a particle size distribution of ca. 4.0±0.5
nm, through the fast reduction of indium(III) chloride in the
presence of lithium sand and a catalytic amount of DTBB,
under mild conditions and in the absence of any anti-
agglomeration additive or ligand. These in situ prepared InNPs
have demonstrated to be very simple and efficient for the
synthesis of homoallylic alcohols from a series of carbonyl
compounds and different allyl halides as allylating agents. As
expected, InNPs demonstrated to be much more efficient than
indium powder, being aldehydes much more reactive than
ketones, yielding the corresponding homoallylic alcohols
6
7
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ARTICLE
Radivoy, M. Volpe, Appl. Catal. A: Gen., 2013, 464-465, 109;
Journal Name
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DOI: 10.1039/C5RA27928C
A mild buttom-up synthesis of indium(0) nanoparticles (4.0±0.5 nm) was developed and efficiently
applied in the allylation of carbonyl compounds.