A Ni-Mg-Al layered triple hydroxide-supported Pd catalyst for heterogeneous acceptorless dehydrogenative aromatization

Article abstract of DOI:10.1039/c7cc01182b

In the presence of a Ni-Mg-Al layered triple hydroxide-supported Pd catalyst, the acceptorless dehydrogenative aromatization of a wide range of cyclohexanols/cyclohexanones and cyclohexylamines efficiently proceeded to give the corresponding phenols and anilines, respectively, in moderate to high yields with the liberation of molecular hydrogen.

Full text of DOI:10.1039/c7cc01182b

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DOI: 10.1039/C7CC01182B
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Ni‒Mg‒Al layered triple hydroxide-supported Pd catalyst for
heterogeneous acceptorless dehydrogenative aromatization†
Xiongjie Jin,*a Kento Taniguchi,a Kazuya Yamaguchi,*a Kyoko Nozakib and Noritaka Mizuno*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
In the presence of a Ni‒Mg‒Al layered triple hydroxide-supported an attractive alternative to produce phenol from benzene, because
Pd catalyst, acceptorless dehydrogenative aromatization of a wide KA oil is industrially produced by the well established two-step
range of cyclohexanols/cyclohexanones and cyclohexylamines procedure involving hydrogenation of benzene to cyclohexane
efficiently proceeded to give the corresponding phenols and followed by aerobic auto-oxidation of cyclohexane (Scheme S1,
anilines, respectively, in moderate to high yields with liberation of ESI†).7 In addition, molecular hydrogen produced in the
molecular hydrogen.
dehydrogenative aromatization step is possibly recycled to the
hydrogenation of benzene (Scheme S1, ESI†). Thus, overall aerobic
oxidation of benzene to phenol should be formally achieved by
these sequential processes. In fine chemical industry, numerous
prominent synthetic methods for substituted phenols and anilines
have been developed, such as electrophilic substitution and cross-
coupling reactions.8 The acceptorless dehydrogenative aromatization
of cyclohexanols/cyclohexanones and cyclohexylamines can be
especially useful for the synthesis of substituted phenols and anilines,
Dehydrogenative aromatization has recently emerged as an
attractive method for the synthesis of various arenes from
ubiquitous saturated six-membered carbocyclic compounds.1 For
example, it has been reported that phenols,2 substituted anilines,3
and aryl ethers4 could be synthesized by employing Pd-catalyzed
dehydrogenative
aromatization
of
cyclohexanones
or
cyclohexylimines as the key reactions. Generally, these reactions
require stoichiometric amounts of oxidants (hydrogen acceptor),
such as 1-octene, styrene, tert-butyl peroxybenzoate, 2,3-dichloro-
5,6-dicyanobenzoquinone, and molecular iodine, or molecular
oxygen.1‒4 On the other hand, acceptorless dehydrogenative
aromatization, which generates molecular hydrogen as the sole co-
respectively,
because
the
easy
availability
of
cyclohexanols/cyclohexanones and cyclohexylamines with various
substituted patterns on cyclohexyl rings through several established
chemical transformations.
Recently, homogeneous Ir- and heterogeneous Pd nanoparticle-
catalyzed acceptorless dehydrogenative aromatization of
cyclohexanones to phenols have been developed.9 However, they
have several drawbacks, such as the need of rather sophisticated
ligands and/or base additives and difficulties in reuse of the
catalysts. Moreover, to the best of our knowledge, there are
virtually no useful catalytic systems for the acceptorless
dehydrogenation of cyclohexanols to phenols and cyclohexylamines
to anilines. Therefore, the development of easily separable and
reusable heterogeneous catalysts for the acceptorless
dehydrogenative aromatization under ligand- and additive-free
conditions is highly desirable from the practical, economical, and
environmental points of view.
product, represents
a more environmentally friendly and
economical method for the synthesis of arenes because of its high
atom efficiency, but has been much less studied until now.
Phenols and anilines are very important commodity chemicals
and also key structural moieties in numerous pharmaceuticals,
agrochemicals, electronic materials, plastics, and resins.5 In bulk
chemical industry, millions tons of phenol are annually produced by
the well known cumene process.6 However, the cumene process
has several shortcomings, such as the formation of acetone co-
product and the involvement of explosive cumene hydroperoxide
(Scheme S1, ESI†).6 The acceptorless dehydrogenative aromatization
of a cyclohexanol/cyclohexanone mixture, namely KA oil, should be
Quite recently, we have reported that the Mg‒Al layered double
hydroxide (LDH)-supported Au‒Pd alloy nanoparticles could
efficiently promote the oxidation of cyclohexanols/cyclohexanones
to phenols using molecular oxygen as the terminal oxidant.2d In a
continuation of our interest in the layered hydroxide-supported
metal catalysts10 for dehydrogenation catalysis, herein, we report
for the first time that a Ni‒Mg‒Al layered triple hydroxide (LTH)-
a Department of Applied Chemistry, School of Engineering,
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp; kyama@appchem.t.u-tokyo.ac.jp;
t-jin@mail.ecc.u-tokyo.ac.jp; Fax: +81-3-5841-7220
b Department of Chemistry and Biotechnology, School of Engineering,
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
† Electronic Supplementary Information (ESI) available: Experimental details,
spectral data of products, Tables S1–S4, Figs. S1–S10, and Schemes S1–S3. See
DOI: 10.1039/x0xx00000x
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supported Pd catalyst can efficiently promote the ligand- and transmission
electron
microscope
(TEM) VaienwaAlyrtsicisle Onlionef
DOI: 10.1039/C7tChCa0t118P2dB
0
additive-free acceptorless dehydrogenative aromatization of Pd(OH)x/Ni1Mg2Al1_LTH after the reaction revealed
cyclohexanols/cyclohexanones to phenols and cyclohexylamines to nanoparticles were formed on the surface of Ni1Mg2Al1_LTH
anilines via a consecutive triple-dehydrogenation process. The (average size of the nanoparticles = 2.7 nm, Fig. S5a, ESI†). The
catalysis was intrinsically heterogeneous, and the catalyst could be Ni1Mg2Al1_LTH support alone did not promote the dehydrogenation
reused several times with keeping its catalytic performance.
(Table S2, entry 11, ESI†). Although the dehydrogenative
also proceeded in the presence of
Initially, we prepared various M‒Mg‒Al layered triple aromatization
hydroxides (M = Ni, Co, Fe, MaMgbAlc_LTH, M/Mg/Al = a/b/c) by the Pd(OH)x/Co1Mg2Al1_LTH and Pd(OH)x/Fe1Mg2Al1_LTH (Table S2,
simple co-precipitation method. Then, MaMgbAlc_LTH supported Pd entries 3 and 4, ESI†), the performance of these catalysts were
hydroxide catalysts were prepared by deposition-precipitation inferior to that of Pd(OH)x/Ni1Mg2Al1_LTH. The effect of the
method (Pd(OH)x/MaMgbAlc_LTH, see the Experimental section in Ni/Mg/Al molar ratio of the support was not significant (Table S2,
ESI† for their preparation and characterization, Table S1 and Fig. S1, entries 5‒7, ESI†). Pd(OH)x/Al2O3, Pd(OH)x/TiO2, and Pd/C were not
ESI†).11 These catalysts were directly applied to the acceptorless effective for the dehydrogenation (Table S2, entries 8‒10, ESI†).
dehydrogenative aromatization of 4-methylcyclohexanol (1a) to 4-
To verify whether the observed catalysis for the
methylphenol (2a) in N,N-dimethylacetamide (DMA) at 150 °C dehydrogenative aromatization was intrinsically heterogeneous or
under 1 atm of Ar (Tables S2 and S3, Figs. S2 and S3, ESI†).12 not, the Pd(OH)x/Ni1Mg2Al1_LTH catalyst was removed by hot
Although Pd(OH)x/Mg3Al1_LDH showed almost no catalytic activity filtration when the conversion of 1a was about 50%, and then the
for
the
dehydrogenation
(Table S2,
entry 1,
ESI†), reaction was carried out under the same reaction conditions with
Pd(OH)x/Ni1Mg2Al1_LTH could efficiently promote the reaction and the filtrate. By the removal of the catalyst, the reaction was
gave the desired 2a in 94% yield (Table S2, entry 2, ESI†); we also completely stopped (Fig. S6, ESI†). Furthermore, inductively coupled
confirmed that ca. three equivalents of molecular hydrogen with plasma atomic emission spectroscopy (ICP-AES) analysis of the
respect to 1a were formed during the reaction. The color of the filtrate revealed that Pd species were not present in the filtrate
Pd(OH)x/Ni1Mg2Al1_LTH catalyst was changed from initial light (below detection limit, Pd: <0.2%). These experimental results
brown to black within less than 1 min. The XPS spectrum of the suggest that the catalysis was not derived from leached Pd species,
freshly prepared Pd(OH)x/Ni1Mg2Al1_LTH catalyst showed the and the observed catalysis was intrinsically heterogeneous.13 The
binding energies of Pd 3d3/2 and 3d5/2 at 341.7 eV and 336.2 eV, Pd(OH)x/Ni1Mg2Al1_LTH catalyst could be easily retrieved from the
respectively, which indicate that the oxidation state of the Pd reaction mixture by simple filtration with >90% recovery, and could
species is +2 (Fig. S4a, ESI†). Aꢀer the catalyst was uꢁlized for the be reused at least five times for the reaction of 1a with keeping its
reaction of 1a for 1 h, the binding energies of Pd 3d3/2 and 3d5/2 high catalytic performance (Figs. S5, S7, and S8 ESI†).14
were changed to 340.5 eV and 335.2 eV, respectively (Fig. S4b, ESI†).
With the optimized reaction conditions in hand, we next
These results suggest that the Pd2+ species were reduced by the investigated the substrate scope of the present acceptorless
substrate to Pd0 species during the reaction. In addition, the dehydrogenative aromatization using Pd(OH)x/Ni1Mg2Al1_LTH as
Table 1 Substrate scope for the acceptorless dehydrogenation of cyclohexanols/cyclohexanones to phenols with Pd(OH)x/Ni1Mg2Al1_LTHa
Entry
15
Substrate
Product
Entry
1
Substrate
Product
Entry
6
Substrate
OH
Product
OH
Entry
11
Substrate
Product
OH
OH
OH
OH
O
OH
Et
Et
EtOOC
EtOOC
10 h, 86%
OH
7 h, 52%
12 h, 89%
OH
10 h, 97%
OH
12
16
O
OH
OH
t-Bu
7
OH
2
3
OH
O
O
t-Bu
N
H
N
H
12 h, 93%
OH
12 h, 92%
OH
16 h, 83%
OH
8
OH
OH
OH
OH
Ph
13
14
O
O
O
O
O
10 h, 94%
OH
Ph
8 h, 76%
Ph
Ph
2 h, 98%
9
10 h, 90%
OH
O
OH
OH
4
5
O
OH
17
18
8 h, 97%
OH
12 h, 95%
OH
10
4 h, 89%
O
OH
OH
0.5 mmol scale: 8 h, 97%
10 mmol scale: 72 h, 88(79)%b
OH
OH
10 h, >99%
5 h, 87%
0.5 h, >99%
aReaction conditions: Substrate (0.5 mmol), Pd(OH)x/Ni1Mg2Al1_LTH (Pd: 1 mol%), DMA (2 mL), 150 °C, Ar (1 atm). Yields were determined by GC analysis
b
using n-hexadecane as the internal standard. Substrate (10 mmol), Pd(OH)x/Ni1Mg2Al1_LTH (Pd: 0.25 mol%), DMA (20 mL), 150 °C, Ar (1 atm), 72 h. The
value in parenthesis is the yield of isolated product.
2 | J. Name., 2012, 00, 1-3
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Table 2 Substrate scope for the acceptorless dehydrogenation of
the catalyst. Various alkyl and phenyl substituted cyclohexanols
were efficiently converted into the corresponding phenols in high
yields (Table 1, entries 2‒10). A 10 mmol-scale dehydrogenation of
3,5-dimethylcyclohexanol was also successful; the amount of the
catalyst could be reduced to 0.25 mol%, and the corresponding
phenol was obtained in 79% isolated yield (Table 1, entry 10). 2-
Cyclohexen-1-ol was also an effective substrate for the
dehydrogenation (Table 1, entry 11). The amide functionality was
tolerated in the present dehydrogenation (Table 1, entry 12).
Besides cyclohexanols, cyclohexanones were also efficiently
dehydrogenated into the corresponding phenols in high yields
(Table 1, entries 13‒16). Cyclohexanones possessing ester and
alkoxy groups were dehydrogenated without hydrolysis of these
functional groups (Table 1, entries 15 and 16). Enones, such as 2-
cyclohexen-1-one and carvone, were also dehydrogenated
efficiently, but the double bond hydrogenation occurred in the case
of carvone (Table 1, entries 17 and 18).
View Article Online
cyclohexylamines to anilines with Pd(OH)x/Ni1Mg2Al1_LTHa
DOI: 10.1039/C7CC01182B
Entry
1
Substrate
Product
Entry
4
Substrate
Product
NH2
NH2
NH2
NH2
10 h, 76%
10 h, 81%
5
6
NH2
NH2
2
3
NH2
NH2
i-Pr
i-Pr
8 h, 95%
NH2
10 h, 83%
NH2
NH2
NH2
t-Bu
t-Bu
10 h, 88%
8 h, 89%
The acceptorless dehydrogenation of cyclohexylamines also
efficiently proceeded in the presence of Pd(OH)x/Ni1Mg2Al1_LTH.
Cyclohexylamines substituted with various alkyl groups on the 2-, 3-,
and 4-positions selectively gave the corresponding anilines in high
yields (Table 2).15 Encouraged by the dehydrogenation catalysis of
Pd(OH)x/Ni1Mg2Al1_LTH, we then attempted the dehydrogenation
of substituted cyclohexenes to arenes (Scheme 1). Cyclohexenes
with cyano and ester groups were efficiently dehydrogenated to the
corresponding arenes in moderate to high yields.16 We also
successfully performed the consecutive two-step Diels-
Alder/dehydrogenation reaction for the synthesis of an arene from
a diene and a dienophile (Scheme 2); the Diels-Alder reaction of
2,3-dimethyl-1,3-butadiene and 1,4-naphthoquinone was carried
out using the heterogeneous Sn‒W mixed oxide catalyst developed
previously by our group,17 and then the dehydrogenation of the
resulting cyclohexene gave 2,3-dimethylathraquinone in 80%
overall yield based on 1,4-naphthoquinone. Furthermore, 4-methyl-
aReaction conditions: Substrate (0.5 mmol), Pd(OH)x/Ni1Mg2Al1_LTH (Pd:
1 mol%), DMA (2 mL), 150 °C, Ar (1 atm). Yields were determined by GC
analysis using n-hexadecane as the internal standard.
CN
CN
1 h, 96% yield
Pd(OH)x/Ni1Mg2Al1_LTH
COOMe
COOMe
9 h, 75% yield
COOMe
COOMe
COOMe
COOMe
7 h, 62% yield
Scheme 1 Dehydrogenation of substituted cyclohexenes catalyzed by
Pd(OH)x/Ni1Mg2Al1_LTH. Reaction conditions: Substrate (0.5 mmol),
Pd(OH)x/Ni1Mg2Al1_LTH (Pd: 5 mol%), styrene (2.0 mmol), DMA (2 mL),
130 °C, Ar (1 atm). Yields were determined by GC analysis using n-
hexadecane as the internal standard.
N-octylaniline
was
succesfully
synthesized
from
4-
methylcyclohexanone and n-octylamine by using the present
acceptorless dehydrogenative aromatization strategy (Scheme S2).
The reaction profile for the Pd(OH)x/Ni1Mg2Al1_LTH-catalyzed
acceptorless dehydrogenation of 1a showed that 4-
methylcyclohexanone (3a) was initially formed, followed by the
dehydrogenation to give 2a (Fig. S9a, ESI†). When the
dehydrogenation of 3a was carried out, 1a was formed as the
intermediate, which suggests that 3a partially works as the
hydrogen acceptor (Fig. S9b, ESI†). The dehydrogenation starting
from 2-cyclohexen-1-one (4b) indicated that phenol (2b) was
produced through the very fast disproportionation of 4b (Fig. S9c,
ESI†). Based on the above results, the present acceptorless
dehydrogenative aromatization proceeds through (a) acceptorless
dehydrogenation of cyclohexanols (1) to cyclohexanones (3)
(Scheme 3a), (b) disproportionation or simple dehydrogenation of 3
to cyclohexenones (4) (Scheme 3b), and (c) disproportionation of
cyclohexenones to give phenols (2) (Scheme 3c).
O
O
O
a)
b)
+
O
O
O
80% yielda
Scheme 2 Consecutive Diels-Alder/dehydrogenation reaction. Reaction
conditions: a) Sn‒W mixed oxide (50 mg), 2,3-dimethyl-1,3-butadiene
(0.75 mmol), 1,4-naphthoquinone (0.5 mmol), dichloromethane (1 mL), rt,
5 h. b) Pd(OH)x/Ni1Mg2Al1_LTH (Pd: 5 mol%), styrene (2.0 mmol), DMA
(2 mL), 130 °C, Ar (1 atm), 1 h. aIsolated yield based on 1,4-naphthoquinone.
deprotonative coordination of 3 to the active metal (Pd) centers.
Pd(OH)x/Mg3Al1_LDH, which is inactive for the dehydrogenation of
1a to 2a, showed almost the same activity as
Pd(OH)x/Ni1Mg2Al1_LTH for the dehydrogenation of 3a to 2a
(Table S4, entries 1 and 2, ESI†). Therefore, the high activity of
Pd(OH)x/Ni1Mg2Al1_LTH for the dehydrogenation of 1 to 2 is likely
originated from its high efficiency for the alcohol dehydrogenation
from 1 to 3 (Scheme 3a). In addition, as mentioned above,
Ni1Mg2Al1_LTH did not promote the dehydrogenation of 1a to 3a
(Table S2, entry 11, ESI†). Thus, we consider that both Pd and Ni
The dehydrogenation of 3a to 2a with various
Pd(OH)x/MaMgbAlc_LTH catalysts were generally more efficient than
Pd(OH)x/Al2O3, Pd(OH)x/TiO2, and Pd/C (Table S4, ESI†), which
indicates that the basicity of MaMgbAlc_LTHs plays a very important
role for the present dehydrogenation likely via promoting
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(a) cyclohexanols to cyclohexanones
Lett., 2013, 15, 2604; (f) Y. Xie, S. Liu, Y. Liu, Y. Wen and G.-J.
Deng, Org. Lett., 2012, 14, 1692; (g) K. TaniguVcihewi,AXrti.cleJiOnn,linKe.
O
OH
DOI: 10.1039/C7CC01182B
Yamaguchi and N. Mizuno, Chem. Commun., 2015, 51, 14969;
(h) K. Taniguchi, X. Jin, K. Yamaguchi and N. Mizuno, Catal. Sci.
Technol., 2016, 6, 3929.
M. Sutter, N. Sotto, Y. Raoul. E. Métay and M. Lemaire, Green
Chem., 2013, 15, 347.
(a) Z. Rappoport, The Chemistry of Phenols, Wiley-VCH,
Weinheim, 2003; (b) H. Fiege, H.-W. Voges, T. Hamamoto, S.
Umemura, T. Iwata, H. Miki, Y. Fujita, H.-J. Buysch, D. Garbe and
W. Paulus, Phenol Derivatives: Ullmann’s Encyclopedia of
Industrial Chemistry, Wiley-VCH, Weinheim, 2012.
(a) M. Weber, M. Weber and M. Kleine-Boymann, Phenol:
Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH,
Weinheim, 2012; (b) J. Wallace, Phenol: Kirk-Othmer
Encyclopedia of Chemical Technology, Wiley-VCH, Weinheim,
2005.
M.T. Musser, Cyclohexanol and Cyclohexanone: Ullmann’s
Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim,
2012.
(a) G. A. Olah, Friedel-Crafts and Related Reactions, Interscience
Publishers, 1963. (b) A. Meijere, F. Diederich, Metal-Catalyzed
Cross-Coupling Reactions, Wiley-VCH, Weinheim, 2004.
(a) S. Kusumoto, M. Akiyama and K. Nozaki, J. Am. Chem. Soc.,
2013, 135, 18726; (b) J. Zhang, Q. Jiang, D. Yang, X. Zhao, Y.
Dong and R. Liu, Chem. Sci., 2015, 6, 4674.
[Pd] + [Ni]
+
H2
R
R
3
1
(b) cyclohexanones to cyclohexenones
4
5
O
O
O
OH
[Pd] + [Ni]
+
+
2 R
R
R
R
3
4
4
1
O
[Pd]
H2
6
R
3
(c) cyclohexenones to phenols
O
OH
O
[Pd]
+
7
8
9
2
R
R
R
4
2
3
Scheme 3 Possible reaction paths for the Pd(OH)x/Ni1Mg2Al1_LTH-catalyzed
acceptorless dehydrogenative aromatization of cyclohexanols.
species are indispensable for the dehydrogenation of 1 to 3
(Scheme 3a). The XPS spectrum of the Pd(OH)x/Ni1Mg2Al1_LTH
catalyst after the dehydrogenation of 1a revealed that Ni species
were not reduced during the reaction and maintained its oxidation
state as +2 (Fig. S10, ESI†). Therefore, Ni2+ species likely assist the
Pd-catalyzed dehydrogenation of 1 to 3. The reaction profile for the
dehydrogenation of 3a to 2a with Pd(OH)x/Mg3Al1_LDH showed
that 1a was not formed as the intermediate (Fig. S9d, ESI†). In
10 (a) K. Motokura, D. Nishimura, K. Mori, T. Mizugaki, K. Ebitani
and K. Kaneda, J. Am. Chem. Soc., 2004, 126, 5662; (b) K. Ebitani,
K. Motokura, T. Mizugaki and K. Kaneda, Angew. Chem. Int. Ed.,
2005, 44, 3423 (c) T. Mitsudome, Y. Mikami, H. Funai, T.
Mizugaki, K. Jitsukawa and K. Kaneda, Angew. Chem. Int. Ed.,
2008, 47, 138; (d) T. Mitsudome, S. Arita, H. Mori, T. Mizugaki, K.
Jitsukawa and K. Kaneda, Angew. Chem. Int. Ed., 2008, 47, 7938;
(e) T. Mitsudome, A. Noujima, Y. Mikami, T. Mizugaki, K.
Jitsukawa and K. Kaneda, Angew. Chem. Int. Ed., 2010, 49, 5545;
(f) A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa and K.
Kaneda, Angew. Chem. Int. Ed., 2011, 50, 2986.
11 The X-ray diffraction (XRD) analysis of Pd(OH)x/MaMgbAlc_LTH
catalysts revealed that the layered structure of the supports
was maintained after the deposition of Pd hydroxide species
(Fig. S1, ESI†).
12 Among the various solvents examined, such as DMA, N,N-
dimethylformamide (DMF), dimethylsulfoxide (DMSO), o-
dichlorobenzene, mesitylene, and diglyme, DMA was the most
suitable solvent for the present dehydrogenation (Table S3,
ESI†).
addition,
Pd(OH)x/Mg3Al1_LDH
did
not
promote
the
dehydrogenation of 1a to 3a, as mentioned above (Table S2, entry 1,
ESI†). Thus, the simple dehydrogenation of 3 to the corresponding 4
proceeds in the case of Pd(OH)x/Mg3Al1_LDH-catalyzed reaction
without occurrence of the disproportionation of 3 (Scheme S3, ESI†).
The above results also indicate that Ni2+ species in the
Ni1Mg2Al1_LTH
plays
an
essential
role
for
the
Pd(OH)x/Ni1Mg2Al1_LTH-catalyzed
disproportionation
of
3
(Scheme 3b). On the other hand, it is likely that Pd species alone are
contributed to the simple dehydrogenation of 3 to 4 and the
disproportionation of 4 (Scheme S3, ESI†).
13 R. A. Sheldon, M. Wallau, I. W. C. E. Arends and U. Schuchardt,
Acc. Chem. Res., 1998, 31, 485.
This work was supported in part by JSPS KAKENHI Grant Number
15H05797 in Precisely Designed Catalysts with Customized
Scaffolding and Grant Number 15H06143.
14 The XRD and TEM analyses of the Pd(OH)x/Ni1Mg2Al1_LTH
catalyst after the 5th reuse experiment revealed that the
Ni1Mg2Al1_LTH structure and the average size of the Pd
nanoparticles were almost unchanged compared to the catalyst
after the 1st dehydrogenation experiment (after the 1st
dehydrogenation experiment: 2.7 nm, after the 5th reuse
experiment: 2.6 nm) (Figs. S5 and S8, ESI†).
Notes and references
1
(a) S. A. Girard, H. Huang, F. Zhou, G.-J. Deng and C.-J. Li, Org.
Chem. Front., 2015, 2, 279; (b) A. V. Iosub and S. S. Stahl, ACS.
Catal., 2016, 6, 8201.
15 K. Taniguchi, X. Jin, K. Yamaguchi, K. Nozaki and N. Mizuno,
Chem. Sci., 2017, 8, 2131.
2
(a) Y. Izawa, D. Pun and S. S. Stahl, Science, 2011, 333, 209; (b) Y.
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DOI: 10.1039/C7CC01182B
Graphic abstract
In the presence of a Ni‒Mg‒Al layered triple hydroxideꢀsupported Pd catalyst, acceptorless dehydrogenative
aromatization of a wide range of substrates efficiently proceeded with liberation of molecular hydrogen.