N-H and S-H insertions over Cu(I)-zeolites as heterogeneous catalysts

Article abstract of DOI:10.1016/j.molcata.2016.02.031

N-H and S-H insertion reactions of α-diazoesters into amines and thiols were conducted using various Cu(I)-zeolites, such as zeolite Y, Y USY, ZSM-5, and beta. All the Cu(I)-zeolites successfully catalyzed N-H insertion reactions with high product yields

Full text of DOI:10.1016/j.molcata.2016.02.031

Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
N–H and S–H insertions over Cu(I)-zeolites as heterogeneous catalysts
Pipas Sahaa, Himchan Jeonb, Pratyush Kumar Mishraa, Hyun-Woo Rheea,∗
,
Ja Hun Kwakb,∗
a Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, South Korea
b Department of Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
N–H and S–H insertion reactions of ␣-diazoesters into amines and thiols were conducted using various
Cu(I)-zeolites, such as zeolite Y, Y USY, ZSM-5, and beta. All the Cu(I)-zeolites successfully catalyzed
N–H insertion reactions with high product yields (70–82%) in aqueous solution at room temperature.
Interestingly, Cu(I)-USY (Si/Al = 30) showed better activity for both N–H and S–H insertion reactions than
Cu(I)-Y (Si/Al = 2.6), even though they have the same structure and the same +1 oxidation state for Cu.
X-ray diffraction, transmission electron microscopy, and X-ray photoemission spectroscopy analysis of
the fresh and used catalysts revealed that no noticeable change in the zeolite structure, oxidation state
of Cu, or sintering of Cu occurred during the reactions. Furthermore, after being recycled four times, the
catalysts showed only minor activity decreases, exhibiting conversion rates 70–80% of those of the fresh
catalysts, demonstrating their stability under the current reaction conditions. Temperature programmed
reduction experiments showed that reduction of Cu+ to Cu◦ occurred at ca. 300 ◦C over Cu(I)-USY, while
it occurred at ca. 800 ◦C over Cu(I)-Y. The significantly higher activity of Cu(I)-USY than Cu(I)-Y may be
due to the more electrophilic Cu centers on Cu(I)-USY, which is highly favorable for ylide formation, and
Received 19 November 2015
Received in revised form 22 February 2016
Accepted 25 February 2016
Available online 27 February 2016
Keywords:
Heterogeneous catalyst
Cu(I)-zeolite
N–H insertion
S–H insertion
therefore facilitates N–H and S–H insertions.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Much research effort has been focused on developing catalytic
reactions based on Cu because it is an abundant and practical alter-
Carbon–heteroatom bond formation is an important challenge
for synthetic chemists because such bonds are present in both nat-
ural and man-made molecules [1,2]. Recently, carbenoid-mediated
carbon–heteroatom bond formation has become of great interest to
the scientific community because carbenoid-based X–H insertions
(XHIs), where X = N, O, S, Se, P, or a halogen, are applicable to both
small molecules and biomolecules [3–7]. The N–H insertion of ␣-
diazocarbonyl compounds into amines using transition metals (Rh,
Cu, Fe, Ru, etc.) is very useful for the synthesis of ␣-amino acid
derivatives, the basic building blocks of proteins [4,7,8]. Further-
more, transition-metal-catalyzed insertions of ␣-diazocarbonyl
compounds into the S–H bonds of thiols is an efficient method for
the construction of C S bonds, which are present in various natural
and synthetic molecules with important biological activities [8,9].
native to precious metal catalysts [7]. Furthermore, there have been
extensive studies to develop immobilized, reusable Cu catalysts
due to their economic and environmental benefits. Therefore, much
effort has focused on developing immobilized Cu catalysts on solid-
support materials, such as clay [10], silica or silica-alumina [11,12],
metal-organic-frameworks [13,14], and polymers [15,16]. Many of
these heterogeneous Cu catalysts exhibited similar or better reac-
tion performances than those of homogeneous Cu catalysts.
Cu(I)-zeolite is a supported catalyst system that, when high-
Si/Al-ratio zeolites are employed, exhibits highly stable Cu+ [17–22]
under aerobic conditions, and they have been employed in vari-
ous Cu-catalyzed reactions. For example, Sommer and Pale have
extensively studied azide-alkyne cycloadditions [23–25], azome-
thine imine cycloadditions [26], multicomponent condensations
[27], homocoupling of alkynes [28], and coupling of alkynes with
amides [29]. Furthermore, Zaccheria et al. have performed C–H
insertion reactions using a heterogeneous Cu/SiO2-Al2O3 catalyst
[11,12].
∗
Corresponding authors.
E-mail addresses: rhee@unist.ac.kr (H.-W. Rhee), jhkwak@unist.ac.kr
Herein, we expand Cu(I)-zeolite-catalyzed reactions to N–H and
S–H insertions with ␣-diazoesters (Scheme 1) with high yields
(J.H. Kwak).
http://dx.doi.org/10.1016/j.molcata.2016.02.031
1381-1169/© 2016 Elsevier B.V. All rights reserved.

P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
11
Scheme 1. Environmentally friendly catalytic N–H and S–H insertion reactions.
(70–82%) in aqueous solution at room temperature. Furthermore,
these heterogeneous catalysts exhibit high stability, allowing them
to be used several times.
during the analysis, a dry ice/acetone trap was included prior to the
detector.
2.3. General procedure for Cu(I)-zeolite catalyzed N–H insertion
of amines with ˛-diazoesters (3a-o)
2. Experimental
2.1. Preparation of the catalysts
In an oven-dried round bottom flask, 1.0 mL of H2O was added
to the Cu(I)-zeolite (100 mg, 0.1 equiv). To this solution, a mixture
of the amine (0.47 mmol, 1 equiv) and the ␣-diazoester (0.47 mmol,
1 equiv) in 1.0 mL t-BuOH was added dropwise, and the reac-
tion mixture was stirred at room temperature for a specified time.
The progress of the reaction was monitored using thin-layer chro-
matography (TLC) with ethyl acetate and hexane as eluents. After
completion of the reaction, it was treated with ethyl acetate. The
Cu(I)-zeolite was collected by centrifugation and washed succes-
sively with water and acetone. After drying under vacuum for 12 h
at room temperature, the catalyst was reused in another reaction.
The ethyl acetate layer was then washed with aqueous 0.3 M NaCl
solution and water. The organic layer was dried over Na2SO4, fil-
tered, and evaporated to leave the crude product, which was then
purified using short-column silica gel chromatography to give the
target compound.
USY (CBV 760, Si/Al = 30), Y (CBV 100, Si/Al = 2.6), ZSM-5 (CBV
3024E, Si/Al = 15), MOR (CBV 10A, Si/Al = 6.5) and zeolite beta (CP
814E, Si/Al = 12.5) were obtained from Zeolyst International Co.
Cu(I)-zeolites were prepared by a previously reported two-step
ion-exchange and thermal treatment method [21]. First, NH4
zeolites were synthesized by solution ion exchange using an
aqueous solution of NH4NO3 (0.1 M). Following ion exchange, the
samples were filtered, washed, and dried at 100 ◦C overnight. All
the catalyst samples were then calcined at 400 ◦C for 12 h under
+
-
+
flowing He (flow rate = 1.0 mL/s) to decompose the NH4 and form
H-zeolites. Solid-state ion exchange of Cu(I) onto the H-zeolites
was accomplished by physical mixing with CuCl in a glove box and
subsequent thermal treatment at 400 ◦C for 2 h under flowing He
(flow rate = 1.0 mL/s). The amount of CuCl were controlled for 3 wt%
of Cu+ of final products. The concentrations of Cu in the zeolites
were confirmed by inductively coupled plasma optical emission
spectroscopy (ICP-OES, Varian, 720-ES) after acid digestion using
hydrofluoric acid. The obtained Cu(I)-zeolites were stored in an
inert atmosphere prior to use.
2.4. General procedure for Cu(I)-zeolite catalyzed S–H insertion
of thiols with ˛-diazoesters (5a-i)
The Cu(I)-zeolite (100 mg, 0.1 equiv) was placed into an oven-
dried round bottom flask, 1and to it 1.0 mL 1,4-dioxane was added.
A mixture of the thiol (0.47 mmol, 1 equiv) and ␣-diazoester
(0.47 mmol, 1 equiv) in 1.0 ml 1,4-dioxane was then added drop-
wise and the reaction mixture was stirred at room temperature for
a specified time. The progress of the reaction was monitored using
TLC with ethyl acetate and hexane as eluents. After completion of
the reaction it was treated with ethyl acetate. The Cu(I)-zeolite was
collected by centrifugation and washed successively with water
and acetone. After drying under vacuum for 12 h at room tempera-
ture, the catalyst was reused in another reaction. The ethyl acetate
mixture layer was then washed with aqueous 0.3 M NaCl solution
and water. The organic layer was dried over Na2SO4, filtered, and
evaporated to leave the crude product, which was purified using
short-column silica gel chromatography to give the target com-
pound.
2.2. Characterization of the catalysts
The crystalline structure of the Cu-zeolites before and after
reaction was confirmed by X-ray diffraction (XRD). XRD patterns
were obtained on a Bruker D8 Advance using CuK␣ radiation
(␭ = 1.5406 Å) in step mode with 2␪ values between 5◦ and 50◦,
with a step size of 0.05◦/s. Transmission electron microscopy
(TEM) images of Cu(I)-zeolites before and after reaction were col-
lected using a JEOL JEM-2100F microscope operated at 200 kV.
TEM samples were prepared by dusting the gently grounded
zeolites samples onto a carbon coated Ni grid. X-ray photo-
electron spectroscopy (XPS) spectra were collected in order to
ascertain the oxidation state of the Cu in the Cu-zeolites using
an ESCALAB-250Xi XPS spectrometer equipped with an Al K␣
radiation source (hv = 1486.6 eV) and using an analysis cham-
ber pressure of ca. 5 × 10−10 mbar. The binding energy (BE)
data were measured by normalizing to the C 1 s transition at
284.6 eV.
2.5. Recoverability testing of Cu(I)-USY
H2-temperature programmed reduction (TPR) measurements
were performed to investigate the nature of the Cu species on the
freshly prepared Cu(I)-zeolites. After solid-state ion exchange at
400 ◦C for 2 h under flowing He (1.0 ml/s), the samples were cooled
to room temperature under continued He flow, and then purged
with 2% H2/Ar (1.0 ml/s) for 1 h at room temperature. After sta-
bilization of the thermal conductivity detector (TCD) signal in a
Hewlett-Packard 7820 gas chromatograph, TPR experiments were
carried out under a flow of 2% H2/Ar (1.0 ml/s) at a heating rate of
10 ◦C/min to 1000 ◦C. To avoid interference from water produced
After the reaction between p-toluidine 1f and methyl 2-diazo-
2-(4-methoxyphenyl) acetate 2b, the reaction mixture was treated
with ethyl acetate. Cu(I)-USY was collected by centrifugation and
washed successively with water and acetone. After drying under
vacuum for 12 h at room temperature, the catalyst was reused
for another reaction between fresh 1f and 2b. This process was
repeated four times, with the product from each cycle being puri-
fied and the yield measured, and the recovered catalyst being
characterized by XRD, ICP, TEM, and XPS.

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P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
Table 1
N–H insertion of 1a to 2aa catalyzed by Cu(I)-zeolites..
Entry
Catalyst
Time (h)
yield (%)
1
2
3
4
5
Cu(I)-USY
Cu(I)-Y
Cu(I)-ZSM5
Cu(I)-MOR
Cu(I)-␤
6
6
6
6
82
68
70
62
35
24
a
Reaction conditions: aniline 1a (1 equiv), methyl 2-diazo-2-phenylacetate 2a (1 equiv), Cu(I)-zeolite (10 mol%) in 2.0 mL of H2O/t-BuOH (1:1 v/v). Yields refer to isolated
yield. The compound was characterized by 1H NMR, 13C NMR, and high-resolution mass spectroscopy.
Table 2
Recoverability of Cu(I)-USY.
Run
Catalyst recoverability (%)
Yield (%)a,b
1
>99
>99
99
80
77
75
70
2c
3c
4c
98
a
Reaction conditions: p-Toluidine 1f (1 equiv), methyl 2-diazo-2-(4-methoxyphenyl) acetate 2b (1 equiv), Cu(I)-USY (10 mol%) in 2.0 mL of H2O/t-BuOH (1:1 v/v) at rt for
6 h.
b
Yields refer to isolated yield.
Recovered catalyst used.
c
2-phenylacetate 2a (1.0 equiv) in H2O/t-BuOH (1:1 v/v) over
Cu(I)-USY (0.1 equiv) at room temperature, and the desired product
3a was obtained in 82% yield. The reaction was also performed in
the presence of other Cu(I)-zeolites, and the results are summarized
in Table 1.
These results show that Cu(I)-USY is the best catalyst for this
transformation. The reaction was also performed in organic sol-
vents such as benzene, toluene, and dichloromethane. Although
3a was formed in similar yields with all solvents assayed, H2O/t-
BuOH was considered the best solvent for this transformation due
to its environmental benignity. Increasing the amount of Cu(I)-USY
from 10 to 20 mol% did not increase the yield of 3a, whereas a low
yield of 3a was obtained when the same reaction was performed
using 5 mol% (0.05 equiv) of Cu(I)-USY. Therefore, 10 mol% Cu(I)-
USY in H2O/t-BuOH (1:1 v/v) was considered to be optimal for this
reaction.
Fig. 1. Powder X-ray diffraction patterns of Cu(I)-USY. (a) Fresh and (b) recovered
after four cycles.
3.2. Recoverability of Cu(I)-USY
We found that Cu(I)-USY showed very robust reaction recov-
erability, affording the N–H insertion product 3f in 70% yield,
with >98% catalyst recovery over four reaction runs (Table 2). This
recycling test indicates the stability of these Cu(I)-zeolite catalysts.
To investigate the reason for their stability, both fresh and recov-
ered catalysts were analyzed by XRD, TEM, XPS, and ICP.
We considered four types of modification that the catalysts
could undergo during the test reactions. Firstly, we considered
changes of the zeolite structures, which was investigated with XRD.
3. Results and discussion
3.1. N–H insertion reactions over Cu-zeolites
To investigate the Cu(I)-zeolite-catalyzed XHIs, we prepared
five representative Cu(I)-zeolites with8 USY, Y, ZSM5, MOR, and
beta to catalyze typical NH insertion reactions with ␣-diazoesters.
Initially aniline 1a (1.0 equiv) was reacted with methyl 2-diazo-

P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
13
Fig. 2. High-resolution TEM images of Cu(I)-USY. (a) Fresh and (b) recovered.
As shown in Fig. 1, the XRD pattern of the recovered catalyst indi-
cates that it has exactly the same crystalline phase as the freshly
prepared catalyst.
Secondly, we considered Cu sintering, which reduces the num-
ber of catalytically active sites. The TEM images shown in Fig. 2a
confirm the homogeneous distribution of Cu(I) species in the USY

14
P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
Table 3
ICP analysis results of fresh and recovered Cu(I)-USY.
Cu(I)-USY
Cu/Al
Cu loading (wt%)
Fresh
Recovered
0.8
0.9
2.6
2.8
zeolite and show no evidence of sintered Cu clusters. TEM images
of spent Cu(I)-USY indicate the same distribution of Cu on the zeo-
lite. Therefore, we concluded that no Cu sintering occurs during test
reactions.
Thirdly, we considered Cu(I) leaching during the reaction, which
could lead to continuous loss of catalytic activity and, more seri-
ously, allow the reaction to occur over the leached Cu+ ions
homogeneously. The results of ICP analysis (Table 3) confirm that
there are no significant changes in Cu loading of the Cu(I)-USY cata-
lyst during reaction. Thus, we concluded that there is no Cu leaching
during the reactions.
Finally, we considered catalyst deactivation through changes in
the oxidation state of the active Cu centers. It is well known that
N–H or S–H insertion is only catalyzed by Cu+, and not by Cu2+
or Cu0. Therefore, if the Cu+ in the zeolites are oxidized to Cu2+
or reduced to Cu0, the catalysts lose their activities. To investigate
the oxidation state of the Cu in the catalysts, we performed XPS
analysis on fresh catalysts, recovered catalysts, and Cu(II)-USY as
a standard. The XPS analysis results (Fig. 3) were used to identify
the Cu ion oxidation state in the fresh and recovered zeolites. In
the fresh Cu(I)-USY, the Cu 2p3/2 peak appears at 933.7 eV, which
clearly indicates the presence of Cu+ ions in the sample. Further-
more, the weak 2p1/2 peak at ca. 953 eV also indicates the presence
of Cu+. The recovered catalyst also exhibits a peak at 934 eV, which
indicates the Cu+ oxidation state. Cu2+ ions result in peaks at ca.
936 eV for 2p3/2 and ca. 956 eV for 2p1/2, and a small satellite peak
at ca. 945 eV. The spectrum of Cu(II)-USY (Fig. 3c) exhibits these
2p3/2 and 2p1/2 peaks, and also some peaks from Cu+ due to the
auto-reduction of Cu2+ that is well known to occur in zeolites dur-
ing XPS data collection. These results clearly indicate the presence
of Cu+ ions in both the fresh and recovered Cu(I)-USY.
The TEM, XRD, ICP, and XPS results are very similar for both
the fresh and recovered Cu(I)-USY, which suggests that Cu(I)-USY
does not undergo significant change, even over four reaction cycles.
These results clearly demonstrate the high stability of Cu(I)-USY
under the reaction conditions employed. Recyclability is one of the
most important advantages of heterogeneous catalysts for practi-
cal applications. While homogeneous catalysts often show superior
activity and selectivity to their heterogeneous analogues, their
practical application is hindered by their cost, which is exacerbated
by the inability to recycle them.
3.3. Expansion of substrate scope
The substrate scope of the current reaction system was inves-
tigated using different amines (Table 4). Aromatic amines give
the corresponding mono-alkylated products 3a-m in good yields
without any side products, as determined from the 1H NMR and
13C NMR spectra of the crude products. Recrystallization of 3a
from chloroform produced single crystals whose structure was
confirmed by X-ray analysis (Fig. 4) [12]. Of the aromatic amines,
aniline gives a higher yield of its corresponding product than the
substituted aromatic amines. The substituents on aromatic ring
have an important effect on this reaction. Aromatic amines having
electron-donating groups on the aromatic ring give higher yields
compared to those having electron-withdrawing groups on the
ring. Conversely, aliphatic amines such as n-butylamine 1n and
cyclohexylamine 1o, do not afford any N–H insertion product under
Fig. 3. Cu 2p XPS spectra of (a) fresh and (b) recovered Cu(I)-USY, and (c) Cu(II)-USY.
these reaction conditions, and the unreacted starting materials are
recovered.
Encouraged by these results, the scope of the reaction was also
investigated using various aliphatic and aromatic thiols. Initially,
4-methylbenzenethiol (4a, 1 equiv) was reacted with methyl 2-
diazo-2-phenylacetate (2a, 1 equiv) in H2O/t-BuOH (1:1 v/v) over
Cu(I)-USY (0.1 equiv) at room temperature. However, only a trace
amount of the S–H insertion product is detected in the 1H NMR
spectrum of the crude product. In contrast, when the same reaction

P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
15
Table 4
N–H insertion reactions between different amines and ␣-diazoesters.a
a
Reaction conditions: amines (1 equiv), ␣-diazoesters (1 equiv), Cu(I)-USY (10 mol%) in 2.0 mL of H2O/t-BuOH (1:1 v/v) at rt for 6 h. Yields refer to isolated yield. The
compounds were characterized by 1H NMR, 13C NMR, and high-resolution mass spectroscopy.
Fig. 4. X-ray crystal structure of inserted product. (A) ORTEP diagram of S–H insertion product 5b. (B) ORTEP diagram of N–H insertion product 3a.
is performed in an organic solvent such as 1,4-dioxane, the desired
S–H insertion product 5a is obtained in 65% yield (Table 5) at room
temperature. Increasing the amount of Cu(I)-USY to 20 mol% (0.2
equiv) has no effect on yield.
Different aliphatic and aromatic thiols were reacted with ␣-
diazoesters under these optimized reaction conditions, and the
results are summarized in Table 5. Both aliphatic and aromatic
thiols give the corresponding products in good yields. Aromatic
thiols with electron-donating groups on the aromatic ring give
higher yields than those having electron-withdrawing groups on
the ring, and aliphatic thiols are better substrates than aromatic

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P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
Table 5
S–H insertion reactions between thiols and ␣-diazoesters.a
a
Reaction conditions: thiols (1 equiv), ␣-diazoesters (1 equiv), Cu(I)-USY (10 mol%) in 2.0 mL of 1,4-dioxane at rt. For aliphatic thiols the reaction time was 6 h, whereas for
aromatic thiols the reaction time was 12 h. Yields refer to isolated yield. The compounds were characterized by 1H NMR, 13C NMR, and high-resolution mass spectroscopy.
thiols. Recrystallization of 5b from chloroform produced single
crystals whose structure was confirmed by X-ray analysis (Fig. 4).
3.4. TPR measurement of Cu(I)-USY
Surprisingly, we found that when other zeolites are used to
support the Cu(I), such as Y, ZSM5, MOR, and ␤, no S–H insertion
product is formed, and in all cases, the unreacted starting materials
are recovered. This is in contrast to the azide-alkyne cycloaddition
results reported by Sommer et al. [11] and the N–H insertion reac-
tion reported here, which is catalyzed by all the Cu(I)-zeolites. We
performed TPR experiments with Cu(I)-USY, Cu(I)-Y, and Cu(II)-Y
as a reference to identify the differences between these zeolites.
As shown in Fig. 5, we found that Cu(I)-USY undergoes reduc-
tion at around 300 ◦C, whereas Cu(I)-Y undergoes reduction above
900 ◦C. The Cu2+ in Y zeolite shows two reduction peaks, one at
300–400 ◦C and one at ca. 900 ◦C, interpreted as Cu2+ to Cu+ and
Cu+ to Cu0 reductions, respectively. Therefore, the reduction peak
at ca. 900 ◦C on Cu(I)-Y can be reasonably attributed to the Cu+
to Cu0 reduction. However, Cu(I)-USY shows two close reduction
Fig. 5. TPR results for Cu(I)-USY (red), Cu(I)-Y (blue), and Cu(II)-Y (black). (For inter-
pretation of the references to colour in this figure legend, the reader is referred to
the web version of this article.)
peaks at ca. 300 ◦C, which is much lower than the second reduction
temperature observed with Cu(I)-Y, and is very close to the Cu2+
to Cu+ reduction temperature observed in Cu(II)-Y. In contrast, the
XPS data (Fig. 3) clearly indicate that the oxidation state of Cu in
Cu(I)-USY is Cu+ exclusively. Therefore, both the reduction peaks in
Cu(I)-USY are interpreted as Cu+ to Cu0 reduction, with the small
reduction temperature difference arising from the Cu being in dif-
ferent positions in the USY zeolite. It is noteworthy that Cu+ ions
in the same zeolite frameworks may exhibit different reduction
temperatures.
We considered that the reduction temperature of the Cu(I)-
zeolites may yield information on the XHIs reaction mechanism.
The reduction of Cu+ to Cu0 is an electron accepting process, so it
is reasonable to assume that low-temperature reduction indicates
superior electrophilicity of a catalyst. Thus, the TPR experiment
indicates that the Cu(I)-USY catalyst is more electrophilic than
Cu(I)-Y. As illustrated in Scheme 2, the XHI reaction proceeds via

P. Saha et al. / Journal of Molecular Catalysis A: Chemical 417 (2016) 10–18
17
zeolite structure, oxidation state of Cu, and sintering of Cu. Catalyst
recycled four times exhibited minor activity decreases (70 to 80%
conversion rates). To the best of our knowledge, this is the first
report of N–H and S–H insertions using zeolite chemistry. All these
results suggest that Cu(I)-USY is a highly active and stable catalyst
for N–H and S–H insertions.
Supporting information
General experimental procedures and spectroscopic data, NMR
spectra (1H and 13C) of all compounds, single crystal X-ray data of
3a and 5b.
Acknowledgements
JHK and HJ acknowledge the Korea Evaluation Institute of
Industrial Technology funded by the Ministry of Trade, Industry
& Energy (10050509) and the Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology (Grant num-
ber 2013R1A1A2009307) for the support of this work. HWR and
PS gratefully acknowledge the Samsung Science and Technology
Foundation (SSTF-BA1401-11). All the authors thank Prof. Myoung
Soo Lah and Mr. Dongwook Kim (UNIST) for solving the X-ray crys-
tal structures.
Scheme 2. Proposed catalytic cycle for N–H and S–H insertions over the Cu(I)-USY
catalyst.
the formation of an ylide intermediate. Therefore, it is assumed that
Cu(I)-USY promotes the formation of a more stable sulfonium ylide
intermediate, thereby facilitating the formation of the S–H inser-
tion product. Conversely, due to their lower electrophilicity, the
other Cu(I)-zeolites are unable to form this sulfonium ylide inter-
mediate, and therefore no S–H insertion occurs with ␣-diazoesters
over these catalysts.
It is noteworthy that our Cu(I)-zeolite affords the mono-
alkylated aromatic amine product in higher yield with better
selectivity than a previously reported homogeneous Cu catalyst,
which produced mixtures of mono- and di-alkylated products [30].
Because of the limited pore size of the zeolite (diameter <10 Å) [31],
only small molecules, such as aniline and the ␣-diazoesters, can
access the reaction sites in the zeolite and couple with each other.
Consequently, the branched mono-alkylated product may not re-
react because it cannot access the catalytic sites. However, when
a homogeneous catalyst is used, the initial reaction product can
further react with another ␣-diazoester. Furthermore, the Cu+ in
homogeneous Cu-catalysts such as Cu(I)-THPTA and Cu(I)-TBTA is
not perfectly stabilized; therefore, when homogeneous catalysts
are used, exclusion of oxygen or a mild reducing agent (e.g. ascor-
bic acid, TCEP) may be required [32]. However, in our study, the
Cu-zeolite reactions were performed under atmospheric conditions
without the addition of any reducing reagents, as the local zeolite
environment stabilizes the Cu+ oxidation state. Thus, we found that
Cu(I)-USY has several advantages over traditional catalysts, which
could make it a practical alternative for N–H and S–H insertion
reactions.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molcata.2016.02.
031.
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18
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