Diethylsilane as a Powerful Reagent in Au Nanoparticle-Catalyzed Reductive Transformations

Article abstract of DOI:10.1002/ejoc.202000483

Diethylsilane (Et₂SiH₂), a simple and readily available dihydrosilane, that exhibits superior reactivity, as compared to monohydrosilanes, in a series of reductive transformations catalyzed by recyclable and reusable Au nanoparticles (1 mol-%) supported on TiO₂. It reduces aldehydes or ketones almost instantaneously at ambient conditions. It can be used in a one pot rapid reductive amination procedure, in which premixing of aldehyde and amine is required prior to the addition of the reducing agent and the catalyst, even in a protic solvent. An unprecedented method for the synthesis of N-arylisoindolines is also shown in the reductive amination between o-phthalaldehyde and anilines. In this transformation, it is proposed that the intermediate N,2-diphenylisoindolin-1-imines are reduced stepwise to the isoindolines. Finally, Et₂SiH₂ readily reduces amides into amines in excellent yields and shorter reaction times relative to previously known analogous nano Au⁽⁰⁾-catalyzed protocols.

Full text of DOI:10.1002/ejoc.202000483

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Diethylsilane as a Powerful Reagent in Au Nanoparticle-
Catalyzed Reductive Transformations
Authors: Anastasia Louka, Marios Kidonakis, Iakovos Saridakis,
Elisavet-Maria Zantioti-Chatzouda, and Manolis Stratakis
This manuscript has been accepted after peer review and appears as an
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using the Digital Object Identifier (DOI) given below. The VoR will be
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202000483
Link to VoR: https://doi.org/10.1002/ejoc.202000483
01/2020

10.1002/ejoc.202000483
European Journal of Organic Chemistry
FULL PAPER
Diethylsilane as a Powerful Reagent in Au Nanoparticle-Catalyzed
Reductive Transformations
Anastasia Louka, Marios Kidonakis, Iakovos Saridakis, Elisavet-Maria Zantioti-Chatzouda and Manolis
Stratakis*
Abstract: Diethylsilane (Et2SiH2), a simple and readily available
dihydrosilane exhibits superior reactivity, as compared to
monohydrosilanes, in a series of reductive transformations catalyzed
by recyclable and reusable Au nanoparticles (1 mol%) supported on
TiO2. It reduces aldehydes or ketones almost instantaneously at
ambient conditions. It can be used in a one pot rapid reductive
amination procedure, in which premixing of aldehyde and amine is
required prior to the addition of the reducing agent and the catalyst,
even in a protic solvent. An unprecedented method for the synthesis
of N-arylisoindolines is also shown in the reductive amination between
o-phthalaldehyde and anilines. In this transformation, it is proposed
that the intermediate N,2-diphenylisoindolin-1-imines are reduced
stepwise to the isoindolines. Finally, Et2SiH2 readily reduces amides
into amines in excellent yields and shorter reaction times relative to
previously known analogous nano Au(0)-catalyzed protocols.
agent tetramethyldisiloxane (TMDS).15 Beyond carbonyl group
hydrosilylation, Yamamoto and co-workers16 have shown that
imines are readily reduced by hydrosilanes in the presence of
catalytic amounts of a AuNPore, actually far more efficiently than
their structurally similar carbonyl compounds. Two other
examples of reductive amination with hydrosilanes appeared later
with a bentonite-gold nanohybrid17 and Au NPs on mesoporous
silica,18 as catalysts. Finally, the activation of hydrosilanes by
nano Au(0) substances has been exploited in the reduction of
amides,19 diazo compounds,20 nitro compounds,21 quinolines,22
and in the cis-semihydrogenation of alkynes.23
Introduction
The catalytic activation of the Si-H bond of hydrosilanes by
transition metals and metallic nanoparticles has been widely
exploited in the past as
a means to generate reactive
intermediates that are capable of reducing organic compounds,
via the hydrosilylation of various functional groups.1 Amongst
these metals, gold has also exhibited catalytic activity. Beyond
ionic Au(I) and Au(III) substances which have shown their ability
in activating hydrosilanes in a limited number of examples,2
surprisingly, Au(0) nanoparticles (Au NPs) and other nano Au(0)
materials were also proven as even more powerful catalysts for
these activation/reaction purposes.3 Thus, typical hydrosilanes
(R3SiH) add to the  bonds of alkynes in the presence of
Au/CeO2,4 Au/Al2O3,5 Au/TiO2,6-7 nano Au film,8 AuNPore,9 or to
Scheme 1. The abnormal reactivity and selectivity of diethysilane (Et2SiH2) in
its Au/TiO2-catalyzed reactions with alkynes and allenes, relative to
structurally similar monohydrosilane (Et3SiH), and our proposal.
a
Besides monohydrosilanes (R3SiH), dihydrosilanes (R2SiH2) have
an unexpected reactivity in the presence of supported Au NPs
(Scheme 1). While the reaction between an alkyne and a typical
monohydrosilane, such as Et3SiH, requires heating at elevated
temperatures for several hours to go to completion, the
structurally similar dihydrosilane Et2SiH2 reacts smoothly at room
temperature within 30 min, however the main product is not the
anticipated hydrosilylation adduct (as occurs with simple
10
allenes (Au/TiO2 and AuPd11 alloy) forming alkenyl silanes.
Carbonyl compounds are readily reduced by hydrosilanes via
nano Au(0)-catalyzed protocols4,12-14 forming silyl ethers, or
alcohols if the produced silyl ethers are readily deprotected under
the reaction conditions. A more efficient protocol was later
provided by our group using Au/TiO2 as catalyst, and as reducing
monohydrosilanes), but
a
dehydrogenative cis-disilylation
pathway is taking place, instead.24 In the case of allenes, an
analogous discrepancy occurs. Although under catalysis by
Au/TiO2, the monohydrosilanes add regioselectively on the more
substituted double bond of a terminal allene,10 with diethylsilane,
mainly a fast dehydrogenative disilylation occurs on the less
substituted double bond.25 The behaviour of Et2SiH2 in the
presence of catalytic amounts of Au nanoparticles is indeed
unique,26 given that searching in the literature it is apparent that
in the presence of any other metal that catalyzes the activation of
silanes, monohydrosilanes and dihydrosilanes do not exhibit any
[a]
Anastasia Louka, Dr. Marios Kidonakis, Iakovos Saridakis, Elisavet-
Maria Zantioti-Chatzouda and Prof. Dr. Manolis Stratakis
Department of Chemistry, University of Crete, Voutes 71003
Heraklion, Greece.
E-mail: stratakis@uoc.gr
Supporting information for this article is given via a link at the end of
the document
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10.1002/ejoc.202000483
European Journal of Organic Chemistry
FULL PAPER
differentiation in product selectivity in their reactions with 
systems. Given the fast catalytic activation of dihydrosilanes by
nano Au(0) catalysts and their unique product selectivity in their
addition to  bonds, we examined in this manuscript the reactivity
of the simple and commercially available diethylsilane (Et2SiH2) in
reductive transformations catalyzed by the also readily available
Au/TiO2. We focus herein on the reduction of carbonyl
compounds, in the process of reductive amination, and in the
challenging reduction of amides into amines.
result justifies the requirement of using at least 1 molar equivalent
of diethylsilane, although it possesses two hydrides. In general,
the analogous labile diethylsilyl ethers can be isolated this way,
only for the case of the reduction of ketones. The reactivity of
diethylsilane is orders of magnitude higher relative to all previous
analogous protocols using simple monohydrosilanes, and is
therefore an appealing reductant for synthetic purposes. ,-
Unsaturated aldehydes and ketones exhibit moderate to good
selectivity toward reduction of the carbonyl group relative to the
double bond (90/10 and 60/40 in the two cases of products 11 and
20). These selectivities are similar to what have been reported
using other hydrosilanes and nano Au catalysts in the past,3h with
the exception of a catalytic system in which Pd atoms were
incorporated either on the AuNPore framework,28a or on a Au
alloy,28b where exclusive 1,4-addition was seen.
Results and Discussion
1. Reduction of aldehydes and ketones
As a common laboratory practice, carbonyl compounds can be
reduced into alcohols using metal hydrides, such as LiAlH4 or
NaBH4, which are pyrophoric and must be handled with
precautions. On the other hand, hydrosilanes can be used as
reducing agents in protocols that are catalyzed by a variety of
metals or Lewis acids.27 As noted in the introduction, nano Au(0)
catalysts were also proven efficient for this purpose, with simple
monohydrosilanes (R3SiH) being not exceedingly reactive.4,12-14
Tetramethyldisiloxane (TMDS) on the other hand was introduced
by our group as a more efficient reductant,15 achieving the
complete reduction of an aryl aldehyde within approximately 40
min at room temperature. To examine the potency of Et2SiH2 as
a reducing agent of carbonyl compounds, we chose initially one
electron rich (p-MeO) and one electron deficient (p-CF3)-
substituted benzaldehyde. To our delight, complete reduction of
both compounds occurred within 1 min at room temperature, in
the presence of 1.5 equiv of Et2SiH2 and 1 mol% Au/TiO2 as
catalyst in dry benzene as solvent, affording the corresponding
alcohols 1 and 2, respectively, in excellent yields (Figure 1). There
is no need for inert atmosphere conditions. Toluene is also a
suitable solvent, however it’s less volatile and more difficult to get
rid of it in the workup. With precisely 1 equiv of Et2SiH2 the
reductions are not often quantitative, most probably due to its
volatility, thus we used a 50% excess of it to ensure the complete
reduction. Apparently the hydrosilylation products (which are
seen by GC-MS analysis of the crude reaction mixture) are very
labile and readily undergo deprotection forming the alcohols,
simply while filtering the crude reaction mixture through a short
pad of silica gel. For larger, gram scale experiments, just after the
reduction was over, the crude reaction mixture was treated by
methanol containing a few drops of acetic acid, prior to filtration.
Following this very promising observation, we examined a series
of aldehydes and ketones (Figure 1) using the same reaction
conditions as described above. All aldehydes and ketones were
quantitatively reduced, irrespectively of any bulkiness, after 1-2
minutes of treatment with diethylsilane. In two specific ketones,
(p-MeO and p-CF3-acetophenone), their labile hydrosilylation
products 14a and 15a respectively (Scheme 2, and Supporting
Information), were quantitatively isolated and characterized via a
fast filtration of the crude reaction mixture through a short pad of
silica gel. No double hydrosilylation products were seen arising
from the further Si-H activation of products 14a and 15a, and this
Figure 1. Rapid reduction of carbonyl compounds by Et2SiH2 catalyzed by
Au/TiO2. [Selectivity of reduction: carbonyl group/double bond = 90/10a, and
60/40b.]
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10.1002/ejoc.202000483
European Journal of Organic Chemistry
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and then adding the reducing agent and the catalyst into the same
flask. The best conditions to achieve the quantitative and smooth
in situ formation of the corresponding imine was by mixing them
in methanol as solvent for 1.5 h at room temperature. To our
surprise, adding into this crude methanol reaction mixture, 1.5
equiv of Et2SiH2 and immediately after 1 mol% Au/TiO2, resulted
to the rapid and quantitative formation of benzylphenylamine, (23
in Figure 2), within less than 1 minute of treatment at ambient
conditions. This reactivity is remarkable, given that diethylsilane
is also rapidly and rather violently decomposed under identical
reaction conditions (in the absence of the imine) by reacting with
methanol, if Au NPs are present. The reaction between
hydrosilanes and alcohols is in general well-established3h in the
field of nano Au(0) catalysis. This observation implies that the
activated on Au NPs dihydrosilane reacts much faster with the
imine than with methanol (which is the reaction solvent, and
apparently in significant excess!). Following this rather
unexpected observation, the same experimental protocol was
applied to a series of aryl aldehydes and anilines, forming the
corresponding secondary benzyl arylamines in very high isolated
yields (Figure 2). In the absence of diethylsilane, and even under
forcing conditions (reflux for 24 h), no reduction is taking place.
Formally, reduction of the imines could have been achieved via a
possible Au NP-catalyzed transfer hydrogenation, with the alcohol
being the hydrogen donor.31
Scheme 2. Isolation of the labile hydrosilylation products 14a and 15a.
2. Reductive amination
Reductive amination is one of the most efficient ways to
synthesize substituted amines starting from carbonyl compounds,
structurally simpler amines and a reducing agent that essentially
reduces the intermediate imine formed from the dehydratative
coupling of the two partners. There is an abundant variation of
protocols in the literature regarding this transformation.29 As
commented in the introduction, Au NPs and other nano Au
substances have been also applied recently as catalysts in
reductive amination processes using as reducing agents
hydrosilanes16-18 or H2.30 The remarkable reactivity of
diethylsilane in the reduction of carbonyl compounds, urged us to
study its suitability as a reducing agent in the process of reductive
amination.
Notably, performing the reduction of benzaldehyde with Et2SiH2
in methanol, instead of benzene (Figure 1), the yields with 1.5
equiv of the reductant were around 40%. This result indicates
indirectly that the reduction of an aldehyde is slower compared at
an analogous imine, allowing thus methanol (solvent) to
decompose the majority of the reducing agent. This observation
is in agreement with a previous report16 on the selective reduction
of imines in the co-existence of aldehydes, using hydrosilanes
and Au NPore as catalyst.
Figure 2. One pot reductive amination of aryl aldehydes with anilines by Et2SiH2
catalyzed by Au/TiO2 in MeOH. (In parentheses are the isolated yields.)
As a key-experiment, we examined the reductive amination
between benzaldehyde and aniline. Instead of preparing and
isolating the corresponding imine, we examined the protocol of
generating the imine simply by mixing the aldehyde and the amine,
Scheme 3. Synthesis of N-arylisoindolines from the reductive amination of o-
phthalaldehyde and anilines, and the proposed mechanism.
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10.1002/ejoc.202000483
European Journal of Organic Chemistry
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Of particular interest is the reductive amination between ortho-
phthalaldehyde and anilines (Scheme 3). Treatment of this
dialdehyde with 2 equiv of anilines in methanol for 1.5 h followed
by reduction of the crude reaction mixture with the diethylsilane
(2.5 equiv)/Au NPs system resulted to the formation of N-
arylisoindolines 41-44 in moderate to very good yields. It has been
molecular sieves 4Å after 6 h. Treatment of this crude mixture with
1.5 equiv of Et2SiH2 and 1 mol% Au/TiO2, also rapidly yields the
amines in very good yields (Figure 3). To facilitate the process,
we added 5-10 equiv of methanol that serves as a proton source
on the nitrogen of the final product. In the case of the reductive
amination of an ,-unsaturated aldehyde (cinnamaldehyde) with
n-butylamine, reduction occurs exclusively on the imine double
bond (product 55), which is in agreement with previous report
established that treatment of ortho-phthalaldehyde with
2
equivalents of anilines generates N,2-diarylylisoindolin-1-imines,
instead of the initially suggested di-imines.32 In a specific example, using AuNPore as catalyst.16 Note that the metal-catalyzed
the isolated after chromatography parent N,2-diphenylisoindolin-
1-imine 41′ was treated with Au/TiO2 and diethylsilane, and it was
cleanly transformed into an equimolar mixture of N-
phenylisoindoline 41 and aniline, apparently via the mechanism
shown in Scheme 3. Isoindolines is a class of compounds with
biological interest,33 and there are many methods available in the
literature regarding their preparation,34 but to best of our
knowledge, our approach is unprecedented. Notably, the recently
reported AuPd/Fe3O4-catalyzed reductive amination method
using the hydrogenation of o-phthalaldehyde in the presence of
nitroarenes (which are precursors of anilines under the reaction
conditions), did not proceed to the formation of N-arylisoindolines,
but stopped at N,2-diarylylisoindolin-1-imines.35 As this bimetallic
AuPd catalytic system was used efficiently in a series of reductive
amination experiments, analogous to those presented in Figure 2,
we emphasize the ability of our system to additionally achieve the
smooth synthesis of N-arylisoindolines.
reduction of analogous conjugated enaminines may suffer from
selectivity issues.36
3. Reduction of amides
A very challenging transformation in organic chemistry is the
reduction of the carbonyl group of amides into -CH2- yielding
amines. Typically, this reduction makes use of highly reactive
metal hydride reductants at elevated temperatures, such as
LiAlH4, however, the search for alternative catalytic methods
using less hazardous reducing agents is a judicious choice. While
the combination of high pressure H2 with several metals has been
applied,37 hydrosilanes38 have been also used as alternative
reducing agents. Apart from many metals (including Co, Zn, Rh,
Ni, and others), nano Au(0) materials are also catalytically active
in the case of hydrosilanes. Thus, Au NPs supported on
o
hydroxyapatite19 provide at 110 C, amines in very good yields.
More recently, an unsupported nanoporous Au material has been
shown as an effective catalyst for this purpose,39 at rather milder
conditions compared to the Au NP
Figure 3. One pot reductive amination of aldehydes/ketones by Et2SiH2
catalyzed by Au/TiO2 in benzene. (In parentheses are the isolated yields.)
With all other combinations of carbonyl compounds and amines,
other than anilines and aryl aldehydes, formation of the
intermediates imines occurs sluggishly in methanol. After some
experimentation, we found that such imines can formed
quantitatively on heating at 70 oC in benzene in the presence of
Figure 4. Reduction of amides into amines by Et2SiH2 catalyzed by Au/TiO2. (In
parentheses are the isolated yields.)
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10.1002/ejoc.202000483
European Journal of Organic Chemistry
FULL PAPER
reductive amination or for the synthesis of the amides were commercially
available.
catalyst. To our delight, using 2 equiv of diethylsilane and 1%
Au/TiO2, a series of amides (Figure 4), including the more
challenging tertiary ones, are cleanly reduced into amines within
1-3 h in benzene as solvent (70 oC). The slowest reductions (3 h)
occur in the cases of the formation of tertiary amines. In the
General procedure for the reduction of carbonyl compounds: To a
dried vial containing the carbonyl compound (0.2 mmole) and diethylsilane
(0.3 mmol) in 0.5 mL of dry benzene, are added at 25 oC, 40 mg of the
catalyst (1 mol% in Au). After 1-2 minutes, the slurry is filtered through a
short pad of silica gel with the aid an additional 2 mL of dichloromethane,
and the volatiles are evaporated under vacuum to provide the alcohols,
which were purified if necessary by a fast column chromatography to get
rid of siloxane by-products. For larger scale experiments and especially in
the case of reducing ketones, methanol containing a few drops of acetic
acid is added prior to the filtration to achieve the deprotection of the silyl
group.
analogous AuNPore-catalyzed protocol,39
a
dihydrosilane
(diphenylsilane) had been used with moderate reactivity, but most
likely this is due to the bulkiness of this specific reducing agent.
Notably, there is only one preceding example in the literature in
which diethylsilane had shown a superior activity relative to simple
hydrosilanes, in the reduction of amides into amines or imines,40
catalyzed by Ir complexes under homogeneous conditions. From
the mechanistic point of view it is more likely that both hydrides of
diethylsilane are involved in this transformation, otherwise more
than 2 molar equivalents of the reducing agent should be
necessary, given that in the case of simple carbonyl compounds
and imines a 50% excess is used. Such scenario has similarities
to the mechanism of reduction of amides by LiAlH4.
Diethyl(1-(4-methoxyphenyl)ethoxy)silane (14a)
Colourless liquid. 1H NMR (500 MHz, CDCl3): 7.27 (d, J = 7.5 Hz, 2H), 6.87
(d, J = 7.5 Hz, 2H), 4.84 (q, J = 6.5 Hz, 1H), 4.42 (quintet, J = 2.5 Hz, 1H),
3.80 (s, 3H), 1.45 (d, J = 6.5 Hz, 3H), 0.99 (t, J = 8.0 Hz, 3H), 0.91 (t, J =
8.0 Hz, 3H), 0.68-0.63 (m, 2H), 0.62-0.56 (m, 2H). 13C NMR (125 MHz,
CDCl3): 158.6, 138.1, 126.6, 113.5, 72.0, 55.2, 26.3, 6.7, 6.6, 5.4, 5.4. MS
(ESI): 238 (M+, 7%), 223 (M+-Me, 48%), 134 (77%), 121 (100%), 91 (83%),
75 (73%). HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for C13H22O2Si+H,
239.1467; found 239.1470.
Finally, we emphasize that in all reductive transformations
described in this manuscript (carbonyl compounds, reductive
amination and amides), the Au nanoparticles on TiO2 are
recyclable and reusable at least in 3 times through a simple
filtration or via a careful decantation of the supernatant solution.
The complete failure of utilizing the hot filtrate after the completion
of any kind of reaction described herein, as a successful reaction
medium via adding in it the substrate and diethylsilane only,
implies that there is no Au leaching into the supernatant solution,
and thus the processes are purely heterogeneous.
Diethyl(1-(4-(trifluoromethyl)phenyl)ethoxy)silane (15a)
Colourless liquid. 1H NMR (500 MHz, CDCl3): 7.58 (d, J = 8.0 Hz, 2H), 7.45
(d, J = 8.0 Hz, 2H), 4.92 (q, J = 6.5 Hz, 1H), 4.43 (quintet, J = 2.5 Hz, 1H),
1.51 (d, J = 6.5 Hz, 3H), 0.99 (t, J = 8.0 Hz, 3H), 0.93 (t, J = 8.0 Hz, 3H),
0.71-0.66 (m, 2H), 0.64-0.58 (m, 2H). 13C NMR (125 MHz, CDCl3): 150.0,
129.2 (JC-F = 32.0 Hz), 125.6, 125.2 (JC-F = 5.0 Hz), 124.3 (JC-F = 270.0
Hz), 71.9, 26.4, 6.6, 6.6, 5.4, 5.4. MS (ESI): 276 (M+, 1%), 261 (M+-Me,
3%), 173 (12%), 153 (100%), 133 (27%), 75 (40%). HRMS (ESI-Orbit trap)
m/z: [M+H]+ calcd for C13H19F3OSi+H, 277.1235; found 277.1228.
General procedure for the reductive amination: To a dried vial are
added 1 equiv of an aryl aldehyde (0.2 mmol) and 1 equiv of an aniline in
0.5 mL of methanol. Following the quantitative formation of imine at 25 oC
(typically 1.5 h), diethylsilane (0.3 mmol) and immediately after the catalyst
(40 mg, 1 mol% in Au) are added. After 1 minutes, the slurry is filtered
through a short pad of silica gel with the aid an additional 2 mL of solvent,
and the volatiles are evaporated under vacuum to provide the amines,
which were purified if necessary by a fast column chromatography to get
rid of siloxane byproducts. For all other carbonyl compounds and amines,
their corresponding imines were formed in benzene containing molecular
sieves 4A (70 oC, 6h). Prior to the addition of the reducing agent and the
catalyst, 5-10 equiv of methanol were added into the same vial. The work
up was the same as above. The spectroscopic data of known products are
provided in the Supporting Information.
Conclusions
In conclusion, we show in this manuscript that diethylsilane
(Et2SiH2) is a superior reagent among all other hydrosilanes in a
series of reductive transformations catalyzed by Au/TiO2.
Carbonyl compounds and imines can be reduced instantaneously
at ambient conditions, and it is remarkable that the reductive
amination can be carried out in methanol as solvent, given that
alcohols also react rapidly with hydrosilanes in the presence of Au
nanoparticles. Our Au nanoparticle-catalyzed reductive amination
procedure provides a simple and unprecedented route for the
synthesis of N-arylisoindolines from the reaction between o-
phthalaldehyde and anilines. The challenging reduction of amides
into amines can be also accomplished, at milder conditions
relative to the known Au-catalyzed protocols. These results are in
accordance with previous observations from our group24,25 that
dihydrosilanes exhibit a unique mode of activation and reactivity
on Au nanoparticles in their reactions with other  systems.
2-(4-Isopropylphenyl)isoindoline (44)
1
White solid (m.p. 165-167 oC). H NMR (500 MHz, CDCl3): 7.35-7.28 (m,
4H), 7.19 (d, J = 8.5 Hz, 2H), 6.64 (d, J = 8.5 Hz, 2H), 4.64 (s, 4H), 2.86
(septet, J = 7.0 Hz, 1H), 1.25 (d, J = 7.0 Hz, 6H). 13C NMR (125 MHz,
CDCl3): 145.4, 138.1, 136.7, 127.3, 127.1, 115.3, 111.5, 53.9, 33.1, 24.3.
HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for C17H19N+H, 238.1596; found
238.1592.
N-(1-(Furan-2-yl)propan-2-yl)butan-1-amine (47)
Colourless liquid. 1H NMR (500 MHz, CDCl3): 7.32 (d, J = 1.5 Hz, 1H), 6.29
(dd, J1 = 2.5 Hz, J2 = 1.5 Hz, 1H), 6.10 (d, J = 2.5 Hz, 1H), 3.21-3.19 (m,
1H), 3.07-3.03 (m, 1H), 2.84-2.68 (m, 3H), 1.64-1.59 (m, 2H), 1.38-1.32
(m, 2H), 1.22 (d, J = 7.0 Hz, 3H), 0.91 (t, J = 7.0 Hz, 3H). 13C NMR (125
MHz, CDCl3): 151.3, 141.8, 110.3, 107.7, 52.8, 45.7, 32.9, 29.7, 29.3, 20.2,
13.6. HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for C11H19NO+H, 182.1545;
found 182.1539.
Experimental Section
Our catalytic system (Au/TiO2) is commercially available and the
nanoparticles have an average size of 2-3 nm. The gold content of the
catalyst is 1% w/w. Prior to its use the catalyst was grinded in a mortar to
become a fine dust. All carbonyl compounds and amines used for
N-(1-(m-Tolyl)ethyl)butan-1-amine (49)
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10.1002/ejoc.202000483
European Journal of Organic Chemistry
FULL PAPER
Colourless liquid. 1H NMR (500 MHz, CDCl3): 7.22 (t, J = 7.5 Hz, 2H), 7.15
(br s, 1H), 7.13 (br d, J = 7.5 Hz, 1H), 7.06 (br d, J = 7.5 Hz, 1H), 3.76 (q,
J = 7.0 Hz, 1H), 2.54-2.42 (m, 2H), 2.35 (s, 3H), 1.52-1.46 (m, 2H), 1.39
(d, J = 7.0 Hz, 3H), 1.32-1.26 (m, 2H), 0.87 (t, J = 7.0 Hz, 3H). 13C NMR
(125 MHz, CDCl3): 138.1, 128.4, 127.8, 127.3, 123.7, 58.4, 47.4, 31.9,
23.9, 21.5, 20.4, 13.9. HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for
C13H21N+H, 192.1752; found 192.1749.
Yamamoto, ChemSusChem 2019, 12, 2936. h) M. Stratakis, I. N. Lykakis,
Synthesis 2019, 51, 2435.
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condenser and the reductant was slowly and dropwise added into the
reaction mixture. The spectroscopic data of known products are provided
in the Supporting Information.
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Acknowledgments
Τhe research work carried out by Anastasia Louka was supported
by the Hellenic Foundation for Research and Innovation (HFRI)
and the General Secretariat for Research and Technology
(GSRT), under the HFRI PhD Fellowship grant (GA. no.31448).
ProFI (FORTH, Heraklion, Greece) is acknowledged for obtaining
the HRMS spectra of the unknown compounds.
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Entry for the Table of Contents
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Au Nanoparticle catalysis
Diethylsilane exhibits remarkable
reactivity relative to typical
hydrosilanes in the reduction of
carbonyl compounds, imines and
amides catalyzed by Au nanoparticles.
Anastasia Louka, Marios Kidonakis,
Iakovos Saridakis, Elisavet-Maria
Zantioti-Chatzouda and Manolis
Stratakis*
Page No. – Page No.
Diethylsilane as a Powerful Reagent
in Au Nanoparticle-Catalyzed
Reductive Transformations
This article is protected by copyright. All rights reserved.