Heterogeneous nickel-catalysed reversible, acceptorless dehydrogenation of N-heterocycles for hydrogen storage

Article abstract of DOI:10.1039/c9cc00918c

Nickel-based nanocatalysts were used in acceptorless, reversible dehydrogenation and hydrogenation reactions of N-heterocycles. Both processes were realized in the same solvent using a single catalyst, without isolation of products and workup, which makes it attractive for hydrogen storage purposes. This concept has been demonstrated in a continuous hydrogenation/dehydrogenation sequence of quinaldine with negligible loss in activity of the nickel catalyst after three hydrogen storage cycles. The scope of acceptorless dehydrogenation has been explored and control experiments suggest that hydrogen liberation is initiated via amine dehydrogenation and supports the direct alkane dehydrogenation from the partially oxidized N-heterocycles.

Full text of DOI:10.1039/c9cc00918c

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DOI: 10.1039/C9CC00918C
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Heterogeneous Nickel-Catalysed Reversible, Acceptorless
Dehydrogenation of N-Heterocycles for Hydrogen Storage
Received 00th January 20xx,
Accepted 00th January 20xx
Pavel Ryabchuk, Anastasiya Agapova, Carsten Kreyenschulte, Henrik Lund, Henrik Junge, Kathrin
Junge and Matthias Beller*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Nickel-based nanocatalysts were used in acceptorless, reversible
dehydrogenation and hydrogenation reactions of N-heterocycles.
Both processes were realized in the same solvent using a single
catalyst, without isolation of products and workup, which makes it
attractive for hydrogen storage purposes. This concept has been
demonstrated in a continuous hydrogenation/dehydrogenation
sequence of quinaldine with negligible loss in activity of the nickel
catalyst after three hydrogen storage cycles. The scope of
acceptorless dehydrogenation has been explored and control
experiments suggest that hydrogen liberation is initiated via
amine dehydrogenation and support the direct alkane
dehydrogenation from the partially oxidized N-heterocycles.
Single catalysts for reverse (de)hydrogenation of N-Heterocycles:
H2
+
Cat.
- H2
N
H
N
Homogeneous catalysts:
OTf
Ph
PPh3
Ir
N
Ir Cl
N
Ir
Cl
F3C
O
N
N
N
N
1
2
3
Fujita
Crabtree
Albrecht
BArF4
Catalytic acceptorless dehydrogenations (CADs) are an
important class of reactions that transform the substrate by
liberation of hydrogen gas. In terms of atom economy and
waste generation this approach has obvious advantages
compared to traditional methods using stoichiometric
H
N
H
N
H
(iPr) P
i
Fe
P( Pr)
2
2
Cy P Co PCy2
2
H B
H
3
CO
CH SiMe
2
3
4
5
1
amounts of oxidant or sacrificial hydrogen acceptors. Hence,
Jones
Jones
apart from synthetic applications, CADs have attracted
attention from the point of “hydrogen economy”, which is a
key technology for chemical hydrogen storage. Among various
Heterogeneous catalysts:
2
- Pt/C(Shimizu)
-
-
Pd, Pt, Rh on SBA-15 (Somorjai and Toste)
Pd-Ni/MIL-100(Fe) (Cai)
liquid organic hydrogen carriers (LOHCs), nitrogen-containing
heterocycles, such as quinolines, are particularly attractive for
- Cu/TiO2 (Kaneda)
- Co SAC/N-doped Carbon (Li and Wang)
storage.3
hydrogen
According to experimental and
-
Ni31Si12/Ni Si@SiO (This work)
2 2
computational studies the presence of the nitrogen atom in
Scheme 1. Single catalysts for acceptorless dehydrogenation and
hydrogenation of N-heterocycles.
0
heterocycles
significantly
decreases
the
ΔH
of
dehydrogenation, compared to their corresponding
The first catalytic system for the reversible
dehydrogenation/hydrogenation of quinoline derivatives using
iridium-based complex 1 was reported by Fujita and co-
workers in 2009. In the past decade a number of homo- and
heterogeneous catalysts has been developed, however most
of them rely on noble metals, such as Ir, Pt, Pd, and Rh.
4
cycloalkanes. Despite significant progress in the development
5
1
of catalytic hydrogenations and dehydrogenations of N-
heterocycles, systems that utilize a single catalyst for both
6
,7
processes are extremely rare.
(Scheme 1). In two cases, high levels of activity were achieved
using earth abundant metal-based homogeneous catalysts,
namely iron and cobalt. Molecular pincer complexes 4 and 5,
studied by the group of Jones, are very attractive, but they are
air- and moisture sensitive and require more expensive
ligands. Development of heterogeneous catalysts based on
a.
Leibniz-Institut für Katalyse e. V. an der Universität Rostock
Albert-Einstein-Straße 29a, 18059 Rostock
E-mail: matthias.beller@catalysis.de
b.
c.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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J. Name., 2013, 00, 1-3 | 1
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non-noble metals is highly desired, yet only two catalytic Table 1. Hydrogenation of quinaldine.a
View Article Online
DOI: 10.1039/C9CC00918C
systems of this kind are known.
4.5 mol% Ni-Cat.
2
Cu nanoparticles supported on TiO reported by Kaneda,
N
a
MeOH/H2O
20°C, 30 atm H2
N
have been used for hydrogenation/dehydrogenation of
quinoline, however besides high metal loading this catalyst
H
1
1
2a
7
d
Conv., %[b]
Yield, %[b]
requires additional activation with H
2
.
Recently, a cobalt
Entry
Ni-Cat.
Cat. A
Cat. B
Cat. C
Cat. D
Cat. E.
single atom catalyst (SAC) stabilized on a nitrogen-doped
carbon matrix has been developed by the group of Wang and
1
2
3
4
5
95
>99
97
93
92
96
24
32
7
e
Li. This material showed good activity, but it was not tested
in the consecutive hydrogenation/dehydrogenations of N-
heterocycles, leaving space for improvements. Besides harsh
reaction conditions and extended reaction times, most of the
29
40
aConditions: 1a (0.5 mmol), 40-45 mg of Ni-Cat. (4.5 mol%), 2 mL
2 2
known catalysts require different solvents for hydrogenation MeOH/H O (1:1), 30 bar H , 16h. [b] Yields and conversions were
determined by GC analysis of the liquid phase, using n-hexadecane as
the internal standard.
and dehydrogenation steps. For practical reasons, both
hydrogen uptake and release ideally should occur in the
presence of the same catalyst in the same reaction.
Therefore, as a part of an ongoing research program
utilizing first-row metal based heterogeneous catalysts for
20 mol% Ni-Cat.
+
2 H2
N
200 °C, Ar
Triglyme
N
1a
H
2a
(
de)hydrogenation reactions, we became interested in
100
Cat. A
Cat. B
Cat. C
Cat. D
Cat. E
development of nickel-based heterogeneous catalysts, which
can be used for hydrogen storage in N-heterocycles. To the
best of our knowledge, catalysts solely based on nickel have
not been used in this type of system. In general, nickel is used
much more frequently for hydrogenations, than for hydrogen
release. So far, the scope for the latter is limited to
80
60
40
20
0
8
9
dehydrogenations
of
alcohols,
ammonia
borane,
1
0
hydrocarbons, and dehydrogenative coupling reactions with
alcohols.11 Herein, we report an intermetallic nickel silicide
catalyst supported on fumed silica (AEROSIL® OX 50), which
promotes the hydrogenation/dehydrogenation of N-
heterocycles.
0
5
10
15
20
25
Time, h
+2AcO-
Figure 1. Dehydrogenation of 2a in the presence of Cat. A-E.
Conditions: 2a (1.25 mmol), 300-500 mg of Ni-Cat. (20 mol%), 5 mL
2
N
N
N
N
N
N
1. Support
2. Drying
production was measured with a manual burette.13
Ni
triglyme, Ar; H
Ni(OAc)2·4H2O
Cat. A - E
2
EtOH, 60 °C, 2 h
Inspired by our preliminary results, we started a systematic
investigation in order to find an efficient catalyst that can be
used for both hydrogenation/dehydrogenation of quinoline
derivatives. Initially, a number of nickel-based materials were
3. Pyrolysis
Ni-Cat.
Cat. A
Cat. B
Cat. C
Cat. D
Cat. E.
Pyrolysis T., C°
Ligand
Support
prepared
Ni−Ligand@Support−Tpyrolysis according to the procedure
Scheme 2).
Among these materials, Ni-phen@SiO
phen@TiO -800 (Cat. C) were identified showing comparable
in
a
similar
fashion
named
1000
800
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
None
SiO
SiO
2
2
(
800
TiO
2
2
-800 (Cat. B) and Ni-
1000
800
SiO
SiO
2
2
2
None
activity to Cat. A for the hydrogenation of quinaldine (Table 1,
see also Table S1). Thus, these three Ni-based catalysts (Cat. A-
C) were examined regarding their efficiency in the reverse
dehydrogenation of 2a. The catalyst activity was evaluated by
measuring the volume of evolved hydrogen gas (Figure 1).
Scheme 2. Preparation of nano-structured Ni-based catalysts studied
in this work.
The catalyst was prepared via impregnation of molecularly-
defined nickel phenanthroline complexes on fumed silica
1
2
support and subsequent pyrolysis at 1000°C. The resulting
material (Cat. A) consists of a Ni Si/Ni31Si12 core and NiO/SiO
shell, covered with N-doped graphene layers: Ni-Si/NiO-
SiO @SiO (Scheme 1). Cat. A catalysed hydrogenation of a
After 24h at 200°C in triglyme, Cat. A gave 74% yield of H
whereas Cat. B and Cat. C showed reduced activity reaching
3% and 53% yield, respectively. The identity of the released
hydrogen was confirmed by GC, with 0.5% of CO and trace
2
,
2
2
6
2
2
2
variety of substrates, including olefins, alkynes, nitroarenes,
ketones and aldehydes, while the dehydrogenations were
studied to a lesser extent.
4
amounts of CO and CH present (< 0.1% each). In our previous
studies on iron and cobalt15 nanocatalysts, we demonstrated
14
that the presence of an N-containing ligand in the preparation
step has a great impact on the catalytic activity. To examine
2
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Cat. A (20 mol% Ni)
Triglyme
the role of 1,10-phenanthroline on the hydrogenation
dehydrogenation of 1a, Cat. D and E prepared in the absence
+
2
View Article Online
2H
N
N
DOI: 10.1039/C9CC00918C
/
H
of ligand were tested. Interestingly, both materials gave only
partial hydrogenation of 1a (Table 1, entries 4 and 5) and failed
to catalyse the reverse dehydrogenation of 2a. Next, the
substrate scope of (de)hydrogenation of N-heterocycles was
studied in the presence of Cat. A (Table 2).
1
00
9
9
98
98
9
7
97
97
8
0
60
4
0
0
0
a
Table 2. (De)hydrogenation of N-heterocycles with Cat. A.
2
2
0 mol%, Cat. A
R
+ 2 H2
R
1H
2DH
3H
4DH
5H
6DH
N
N
H
2
1
Figure 2. Catalyst reusability and reversible hydrogen storage with 1a
1.25 mmol), 500 mg Cat. A (20 mol% Ni), 5 mL triglyme.
Hydrogenation (H): 120°C, 50 bar H , 16h Dehydrogenation (DH);
(
Dehydrog.:
Yield, % [b]
Hydrog.: Yield,
(Conv.)% [d]
2
Substrates
H
2
2
00°C, Ar, 48h. The hydrogen uptake and release values were
calculated by GC analysis of the liquid phase of 1a and 2a and based on
the preceding step.
7
4 (93[c]
)
93 (100)
N
N
H
2a
1a
57
50
62
91 (100)
N
N
H
2
b
1b
NH
N
NA[e] (80)
2c
1c
92 (100)
N
N
H
2
d
1d
[
2
a] Dehydrogenation: 2 (1.25 mmol), 500 mg of Cat. A (20 mol%),
00°C, 24 h. 5 mL triglyme, Ar.; Hydrogenation: 1 (0.25 mmol), 100 mg
of Cat. A (20 mol%), 2 mL triglyme, 120°C, 50 bar H , 16h; [b] H
production was measured with a manual burette; [c] H production
2
2
2
measured after 48 hours [d] Yields and conversions were determined
by GC analysis of the liquid phase, using n-hexadecane as the internal
standard; [e] NA = not available, GC signal for 2c overlaps with
triglyme.
Dehydrogenation of various heterocycles was monitored
by gas evolution in the first 24 h of the reaction.
Tetrahydroquinaldine 2a gave 74% of the maximum hydrogen
quantity, while homologous 2b reached only 57%. The methyl
substitution of the aromatic ring in 2d resulted in increased
hydrogen evolution: 62% after 24 h. Notably, 1,2,3,4- Figure 3. (a,b) STEM images of Cat. A after 3 hydrogenation-
dehydrogenation cycles. The annular bright field (ABF) image (a) shows
the presence of nanoparticles covered by a graphitic structure, while
high angle annular dark field (HAADF) image (b) displays metallic Ni
particles with irregular shape. STEM images (c,d) of Cat. A after a
tetrahydroisoquinoline 2c showed the lowest rate, reaching
only 50% conversion after 24 hours. As shown above,
complete conversion of 1a to 2a can be achieved with 4.5
mol% Cat. A at 30 bar H
2
in methanol-water mixture, however single dehydrogenation, demonstrate the presence of similar metallic
Ni particles (d), while also some nanoparticles graphite-covered are
hydrogenation in triglyme requires higher hydrogen pressure
and catalyst loading. With exception of 1c, all N-heterocycles
can be fully hydrogenated both in methanol-water and
triglyme. Based on the rate of dehydrogenation of 2a, 1a/2a
were selected as model substrates for hydrogen storage. Initial
hydrogenation of 1a was performed in triglyme using 20 mol%
of Cat. A in a steel autoclave with a mechanical stirrer. Upon
completion of the reaction, without workup or any other
manipulations, the obtained product 2a was dehydrogenated
at 200 °C in the same autoclave. The hydrogen uptake/release
was demonstrated for three consecutive cycles with no loss in
reactivity (Figure 2). Although atomic absorption spectroscopy
present (c).
(de)hydrogenation step, upon three consecutive cycles small
amounts of nickel were detected in solution (~20 ppm).
Even though Cat. A showed no noticeable deactivation
after 3 cycles, analysis of the material revealed structural
changes in the catalyst. STEM images of Cat. A were acquired
at different stages and are shown in Figure 3 (Figures S1-S8).
Apart from nickel nanoparticles covered by a graphitic
structure (a), large metallic nickel particles with irregular
shapes were formed (b). Intrigued by these unexpected
changes in the material structure compared to the fresh
1
2
catalyst , we examined Cat. A after a single hydrogenation of
(AAS) revealed no measurable leaching after a single
1
a and a single dehydrogenation of 2a. Upon hydrogenation,
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nickel silicide particles remained, as judged by XRD (Figure S9), under optimized conditions. Preliminary mechanViieswtiAcrticslteuOdnilienes
and no strongly irregular-shaped Ni(0) particles were formed are evident of the initial amine-dehydDrOoI:g1e0n.1a0t3io9/nC9sCtCe0p09a1n8Cd
(Figures S7, S8) although quite compact Ni(0) particles were support the direct alkane dehydrogenation from the partially
present. Relatively large and irregular shaped Ni(0) appeared oxidized N-heterocycles.
only after or during the dehydrogenation process (Figure 5(d),
Figures S3-S6). Since no significant loss in activity has been
observed, we suggest that these Ni(0) particles are catalytically
Conflicts of interest
active for the (de)hydrogenation of N-heterocycles.
There are no conflicts to declare.
2
0 mol% Cat. A
(1)
N
R
200 °C, 24h
N
R
Notes and references
R = Me (2e)
R = Ac (2f)
1
2
3
4
C. Gunanathan, D. Milstein, Science, 2013, 341, 1229712.
Q.-L. Zhu, Q. Xu, Energy Environ. Sci., 2015, 8, 478-512.
R. H. Crabtree, Energy Environ. Sci., 2008, 1, 134-138.
2
0 mol% Cat. A
or
(2)
N
200 °C, 24h
X
(a) E. Clot, O. Eisenstein, R. H. Crabtree, Chem. Commun., 2007, 0,
2g
2h
X = CH or N
2
231-2233; (b) A. Moores, M. Poyatos, Y. Luo, R. H. Crabtree, New J.
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M. Wiesenfeldt, Z. Nairoukh, T. Dalton, F. Glorius, Angew. Chem., Int.
Ed., 2019, doi:10.1002/anie.201814471
2
0 mol% Cat. A
5
6
(3)
200 °C, 24h
2i
77%
(a) R. Yamaguchi, C. Ikeda, Y. Takahashi, K.-i. Fujita, J. Am. Chem. Soc.,
2
009, 131, 8410-8412; (b) M. G. Manas, L. S. Sharninghausen, E. Lin,
R. H. Crabtree, J. Organomet. Chem., 2015, 792, 184-189; (c) Á.
Vivancos, M. Beller, M. Albrecht, ACS Catalysis, 2017, 8, 17-21; (d) S.
Chakraborty, W. W. Brennessel, W. D. Jones, J. Am. Chem. Soc., 2014,
Path A
1st
2nd
1
36, 8564-8567; (e) R. Xu, S. Chakraborty, H. Yuan, W. D. Jones, ACS
dehydrogenation
dehydrogenation
Catalysis, 2015, 5, 6350-6354.
N
N
N
7
(a) S. K. Moromi, S. M. A. H. Siddiki, K. Kon, T. Toyao, K.-i. Shimizu,
Catal. Today, 2017, 281, 507-511; (b) C. Deraedt, R. Ye, W. T. Ralston,
F. D. Toste, G. A. Somorjai, J. Am. Chem. Soc., 2017, 139, 18084-
H
1a
3a
2
a
N
1
8092; (c) J.-w. Zhang, D.-d. Li, G.-p. Lu, T. Deng, C. Cai,
H
3a'
Path B
ChemCatChem, 2018, 10, 4966; (d) K. Kaneda, Y. Mikami, T.
Mitsudome, T. Mizugaki, K. Jitsukawa, Heterocycles, 2010, 82, 1371;
Scheme 3. Control experiments and proposed reaction mechanism.
To get insights into the mechanism of nickel-catalysed
dehydrogenation of heterocycles, control experiments with
selected substrates have been performed (Scheme 3). Two
substrates bearing a protected nitrogen atom 2e and 2f do not
react in the dehydrogenation (eq 1). These results clearly show
the important role of a free N-H group in the dehydrogenation
process. Moreover, isomeric 5,6,7,8-tetrahydroquinoline 2g
with no saturated C-N bonds failed to produce 1b. As
expected, a carbon analogue tetraline 2h does not react under
(
e) Y. Han, Z. Wang, R. Xu, W. Zhang, W. Chen, L. Zheng, J. Zhang, J.
Luo, K. Wu, Y. Zhu, C. Chen, Q. Peng, Q. Liu, P. Hu, D. Wang, Y. Li,
Angew. Chem., Int. Ed., 2018, 57, 11262-11266.
(a) Z. Dai, Q. Luo, H. Jiang, Q. Luo, H. Li, J. Zhang, T. Peng, Catal. Sci.
Technol., 2017, 7, 2506-2511; (b) G. Liang, L. He, H. Cheng, W. Li, X. Li,
C. Zhang, Y. Yu, F. Zhao, J. Catalysis, 2014, 309, 468-476.
(a) M. O. Talbot, T. N. Pham, M. A. Guino-o, I. A. Guzei, A. I. Vinokur,
V. G. Young, Polyhedron, 2016, 114, 415-421; (b) P. M. Zimmerman, A.
Paul, Z. Zhang, C. B. Musgrave, Angew. Chem., Int. Ed., 2009, 48,
8
9
2
201-2205.
O. S. Al-Ayed, D. Kunzru, J. Chem. Technol. Biotechnol., 1988, 43, 23-
8.
1
1
0
1
3
optimized
reaction
conditions.
However,
1,2-
on
(a) S. Parua, S. Das, R. Sikari, S. Sinha, N. D. Paul, J. Org. Chem., 2017,
82, 7165-7175; (b) S. Parua, R. Sikari, S. Sinha, S. Das, G. Chakraborty,
N. D. Paul, Org. Biomol. Chem., 2018, 16, 274-284; (c) S. Parua, R.
Sikari, S. Sinha, G. Chakraborty, R. Mondal, N. D. Paul, J. Org. Chem.,
dihydronapthalene 2i yield 77% of naphthalene. Based
the results above, we propose, that the dehydrogenation
sequence starts with the release of one equivalent of H , from
2
2
018, 83, 11154–11166.
the C-N bond, giving intermediate 3a. Further
dehydrogenation can proceed in two different scenarios: via
1
2
P. Ryabchuk, G. Agostini, M.-M. Pohl, H. Lund, A. Agapova, H. Junge,
K. Junge, M. Beller, Sci.Adv., 2018, 4, eaat0761.
direct alkane dehydrogenation (Path A) or via tautomerization 13 Gas evolution curve for Cat. A was obtained from a set of 5 identical
experiments, which were reported in Ref. 11.
to 3a’ and subsequent dehydrogenation from the secondary
1
4
Fe: (a) Jagadeesh, R. V.; Surkus, A.-E.; Junge, H.; Pohl, M.-M.; Radnik,
J..; Rabeah, J.; Huan, H.; Schünemann, V.; Brückner, A.; Beller, M.
Science, 2013, 342, 1073–1076. (b) Ryabchuk, P.; Junge, K.; Beller, M.
Synthesis, 2018, 50, 4369-4376. (c) Cui, X.; Li, Y.; Bachmann, S.;
Scalone, M.; Surkus, A. E.; Junge, K.; Topf, C.; Beller, M. J. Am. Chem.
Soc., 2015, 137, 10652−10658.
Co: (a) Westerhaus, F. A.; Jagadeesh, R. V.; Wienhöfer, G.; Pohl, M.-
M.; Radnik, J..; Surkus, A.-E.; Rabeah, J.; Junge, K.; Junge, H.; Nielsen,
M.; Brückner, A.; Beller, M. Nat. Chem., 2013, 5, 537–543. (b) Chen,
F.; Kreyenschulte, C.; Radnik, J.; Lund, H.; Surkus, A.-E.; Junge, K.;
Beller, M. ACS Catal., 2017, 7, 1526–1532. (c) Chen, F.; Topf, C.;
Radnik, J.; Kreyenschulte, C.; Lund, H.;Schneider, M.; Surkus, A.-E.; He,
L.; Junge, K.; Beller, M. J. Am. Chem. Soc., 2016, 138, 8781−8788.
amine fragment as postulated by Jones (Path B). Based on the
activity of 2i, which is structurally relevant to 3a, direct
dehydrogenation of 3a to 1a via Path A is possible. We believe
that the liberation of the second equivalent of H
2
occurs via
both reaction pathways.
1
5
In summary, we demonstrated the first heterogeneous
nickel nanostructured catalyst (Cat. A) capable of promoting
hydrogenation and dehydrogenation of N-heterocycles. This
robust, reusable, and highly efficient material allows for
hydrogen storage in quinoline derivatives. The hydrogen
uptake/release was demonstrated for three consecutive cycles
4
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View Article Online
DOI: 10.1039/C9CC00918C
+
H2
Ni-NP Catalyst
N
N
H
- H2
Reversible Dehydrogenation/Hydrogenation
Nickel catalyst for hydrogen storage in N-heterocycles: A heterogeneous nickel catalyst
promotes both hydrogenation and subsequent dehydrogenation of quinoline derivatives.