Heterogeneous Ru/TiO2for hydroaminomethylation of olefins: multicomponent synthesis of amines

Article abstract of DOI:10.1039/d1gc00113b

Synthesizing aminesviathe hydroaminomethylation (HAM) reaction of olefins, a multicomponent reaction, has been regarded as one of the most attractive methods compared with the traditional methods considering the atom economy and environmental friendliness. However, the use of homogeneous catalysts, complex ligands containing diphosphine or nitrogen, and base or acid additives has severely hampered the utilization of these methods. Herein, an efficient heterogeneous Ru/TiO₂-catalyzed HAM reaction of olefins is developed without any additives. Various amines, including secondary and tertiary amines, can be successfully obtained from olefins including aromatic and aliphatic olefins. Systematic studies demonstrate the lower electron density of Ru^δ+and the higher number of acid sites of Ru/TiO₂, leading to the high HAM reaction activity of olefins. Most importantly, nitrobenzene derivatives can also be transformed to the corresponding products over Ru/TiO₂in excellent yields.

Full text of DOI:10.1039/d1gc00113b

Green Chemistry
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PAPER
Heterogeneous Ru/TiO2 for hydroaminomethyl-
ation of olefins: multicomponent synthesis of
amines†
Cite this: Green Chem., 2021, 23,
2722
b
Jinghua An, a,b Zhuyan Gao, b,c Yehong Wang, b Zhixin Zhang,
b
Jian Zhang,b Lu Li,a Bo Tanga and Feng Wang
*
Synthesizing amines via the hydroaminomethylation (HAM) reaction of olefins, a multicomponent reac-
tion, has been regarded as one of the most attractive methods compared with the traditional methods
considering the atom economy and environmental friendliness. However, the use of homogeneous cata-
lysts, complex ligands containing diphosphine or nitrogen, and base or acid additives has severely ham-
pered the utilization of these methods. Herein, an efficient heterogeneous Ru/TiO2-catalyzed HAM reac-
tion of olefins is developed without any additives. Various amines, including secondary and tertiary
amines, can be successfully obtained from olefins including aromatic and aliphatic olefins. Systematic
studies demonstrate the lower electron density of Ruδ+ and the higher number of acid sites of Ru/TiO2,
leading to the high HAM reaction activity of olefins. Most importantly, nitrobenzene derivatives can also
be transformed to the corresponding products over Ru/TiO2 in excellent yields.
Received 11th January 2021,
Accepted 2nd March 2021
DOI: 10.1039/d1gc00113b
rsc.li/greenchem
of the aldehyde with the substrate amine; and (iii) the for-
mation of the target product amine via the hydrogenation reac-
Introduction
Amines, acting as the ubiquitous building blocks for the tion of the imine or enamine. Although some homogeneous
essential pharmaceutically and biologically active compounds, catalytic systems have been reported in recent years, some
dyes, and agrochemicals, are one of the most important limitations such as the use of homogeneous catalysts, ligands
N-containing compounds.1 As
a
consequence, various containing diphosphine or nitrogen, base or acid additives
methods for synthesizing amines have been developed with have severely hampered the further utilization of these
their increasing global demand. Compared with the traditional methods. For example, the general catalytic system utilizing
methods, including carbonyl reductive amination,2 amination expensive Rh compound for the HAM reaction of olefins was
of alcohols,3 and hydrogenation of amides,4 the hydroamino- reported by Beller’s group (Scheme 1a, i).6 Their continuing
methylation (HAM) reaction of olefins has become one of the works using a relatively cheaper homogeneous Ru-catalyzed
most attractive methods to produce amines considering the HAM reaction of olefins have also been reported;7 high
atom economy and environmental friendliness.
product yields could be obtained only when the inorganic base
The HAM reaction of olefin was reported by Reppe5 and was added into the system (Scheme 1a, i). Recently, a Rh-based
involved the following three steps: (i) the formation of an alde- complex catalyst with phosphoric acid as a co-catalyst was used
hyde via the hydroformylation reaction of olefin; (ii) the for- in the HAM reaction of olefins by Han’s group,8 which was a
mation of an imine or enamine via the condensation reaction pioneering work. However, low yields were obtained when ali-
phatic olefins were used as substrates (Scheme 1a, ii).
Unlike the above catalytic systems,
a multicatalytic
aCollege of Chemistry, Chemical Engineering and Materials Science, Key Laboratory
of Molecular and Nano Probes, Ministry of Education, Collaborative Innovation
Center of Functionalized Probes for Chemical Imaging in Universities of Shandong,
Institute of Molecular and Nano Science, Shandong Normal University, Jinan
250014, P. R. China
bState Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy,
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023,
PR China. E-mail: wangfeng@dicp.ac.cn
approach was developed to produce amines under mild reac-
tion conditions by Hartwig’s group (Scheme 1b).9 However,
two distinct catalysts used in the catalytic system made the
reaction more complex. In addition, Shukla’s group reported
that rhodium-exchanged titanosilicates were effective hetero-
geneous catalysts for the hydroaminomethylation reaction
with limited substrate tolerance (Scheme 1c).10 Therefore,
developing an efficient and greener catalytic system, wide sub-
strate tolerance, for synthesizing amines via the HAM reaction
cUniversity of Chinese Academy of Sciences, Beijing, 100049, PR China
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1gc00113b
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Table 1 Synthesis of N-(cyclohexylmethyl) aniline (1) from aniline,
a
cyclohexene, CO, and H2
Yield
of 1, %
Yield
of 1, %
Entry
Catalyst
Entry
Catalyst
1
2
3
4
5
6
7
8
No catalyst
TiO2
0
0
58
28
27
15
0
9
Ru/MgO
Ru/CeO2
Rh/TiO2
Pd/TiO2
Ir/TiO2
RuCl3·nH2O
Ru/TiO2
Ru/TiO2
9
34
0
0
10
11
12
13
14
15
16
Ru/TiO2
Ru/TiO2-R
Ru/TiO2-A
Ru/ZnO
Ru/WO3
Ru/Al2O3
0
14
91b(84c)
70d
36
a Reaction conditions: catalyst (0.1 g), aniline (0.4 mmol), cyclohexene
(1.0 mmol), CO (0.5 MPa), H2 (0.5 MPa), THF (2.0 mL), 160 °C, 3 h.
Conversion was determined by GC using n-dodecane as an internal
standard. b 4 h. c Isolated yield. d 4.5 h, the decrease of the yield of 1
was owing to the production of tertiary amine resulting from the
further reaction of 1.
Scheme 1 Catalytic systems for the synthesis of amines via the HAM
reaction of olefins.
of olefins is desirable but challenging in both scientific and
commercial significance.
decreased to 70% with the formation of a tertiary amine owing
to the further reaction of 1, indicating that secondary and ter-
tiary amines can be easily obtained just by controlling the reac-
tion time (Table 1, entry 16). The Ru/TiO2 catalyst could be
easily retrieved by simple filtration and reused at least four
times with a decrease in the activity (Fig. S1(a)†). The reaction
was stopped once the Ru/TiO2 catalyst was removed in 2 h,
indicating that this reaction was heterogeneous catalysis (Figs.
S1(b), S2(a), S2(b), and S2(c)†).
Recently, Ru-based heterogeneous catalytic systems have
been reported to synthesize esters and quinazolinones from
the carbonylation reaction of olefins by our group.11
Considering their excellent activities in carbonylation reac-
tions, Ru-based heterogeneous catalysts then entered into our
line of sight and were used to catalyze the HAM reaction of
olefins (Scheme 1d). Fortunately, a Ru/TiO2 catalyst was found
to show excellent catalytic activity on the HAM reaction of
olefins.
Scope of substrates
Delighted by the high catalytic activity of Ru/TiO2 on the syn-
thesis of 1 from aniline, cyclohexene, CO, and H2 (Table 1,
entry 15), the activities of other amines or olefins were then
Results and discussion
Initially, the synthesis of N-(cyclohexylmethyl) aniline (1) was tested under the optimized reaction conditions (Tables 2
conducted with tetrahydrofuran (THF) as a solvent and and 3). 16 secondary amines and 8 tertiary amines could be
aniline, cyclohexene, CO, and H2 as substrates (Table 1). In the synthesized in moderate to excellent yields using less reactive
absence of a catalyst or only in the presence of the support cyclohexene, primary or secondary amine as substrates in the
TiO2, no products were obtained (Table 1, entries 1 and 2). presence of CO and H2 (Tables 2(i) and (ii)). The investigation
Excitingly, when Ru-supported TiO2, consisting of 80% demonstrated that substituents including electron-donating
anatase and 20% rutile, was used as a heterogeneous catalyst, groups (–CH3 or –OCH3) and -withdrawing groups (–Cl or –F)
the target product 1 could be obtained with 58% conversion of at the para-position of anilines have little effect on the reaction
aniline and >99% selectivity (Table 1, entry 3). Other common activity (Table 2(i), 1a–4a: 72%–97%). Substituents could also
oxide supports such as pure rutile TiO2 (TiO2-R), pure anatase be tolerated at the ortho-position of anilines except for
TiO2 (TiO2-A), ZnO, WO3, Al2O3, MgO, and CeO2 showed poor o-methoxy aniline, possibly owing to the steric effect (Table 2(i),
performance (Table 1, entries 4–10). Other metals, including 5a–8a: 60%–97%; 6a: 60%). Meanwhile, the reactivity of
Rh, Pd, and Ir, had no catalytic activity (Table 1, entries anilines with two substituents at the ortho-position follows the
11–13). A low yield of 1 (14%) was obtained when RuCl3·nH2O, order 2,6-dimethyl aniline (9a: 96%) > 2,6-diethyl aniline (10a:
the precursor of Ru/TiO2, was used as a catalyst for comparison 75%) > 2,6-dimethoxy aniline (11a: 41%), confirming the exist-
(Table 1, entry 14).
ence of the steric effect. In addition, other aromatic amines,
Extending the reaction time to 4 h, the yield of 1 could including furfuryl amine, 1-naphthylamine, and benzylamine,
reach 91% and the isolated yield was 84% (Table 1, entry 15). could be transformed to the corresponding products in excel-
1
The H NMR and 13C NMR spectra of 1 are given in the ESI.† lent yields (Table 2(i), 12a–14a: 81%–92%). Cyclohexylamine,
Further extending the reaction time to 4.5 h, the yield of 1 acting as an aliphatic amine, is even compatible with the reac-
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a
Table 2 Synthesis of secondary amines and tertiary amines from various amines, cyclohexene, CO, and H2
a Reaction conditions: Ru/TiO2 (0.1 g), amine deviation (0.4 mmol), cyclohexene (1.0 mmol), H2 (0.5 MPa), CO (0.5 MPa), 160 °C, 12 h. Yields
were isolated yields, and the corresponding 1H NMR and 13C NMR spectra of the products are given in the ESI.† b 8 h. c 10 h. d 9 h. e GC yield.
a
Table 3 Synthesis of amines from aniline, various olefins, CO, and H2
a Reaction conditions: Ru/TiO2 (0.1 g), aniline (0.4 mmol), olefin (1.0 mmol), H2 (0.5 MPa), CO (0.5 MPa), THF (2.0 mL), 160 °C, 23 h. b Combined
yields. c 12 h. d Olefin (0.5 MPa), 6 h. Yields were isolated yields, and the corresponding 1H NMR and 13C NMR spectra of the amines are given in
the ESI.† The formation of tertiary amines resulted from the further reaction of secondary amines. e Cyclopentene was used as the substrate.
tion (Table 2(i), 15a: 99%), while n-hexylamine gave a moderate amines were used as substrates (Table 2(ii)). N-Methyl aniline
product yield (Table 2(i), 16a: 63%).
and N-ethyl aniline gave excellent product yields (Table 2(ii),
In addition to secondary amines, tertiary amines could also 17a: 99%; 18a: 85%), while N-phenyl aniline gave a lower
be obtained in moderate to high yields when secondary product yield (Table 2(ii), 19a: 45%), owing to the increase of
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steric hindrance. With secondary benzylic amine as a sub-
strate, 99% product yield was achieved (Table 2(ii), 20a: 99%).
Indoline also underwent this transformation, albeit in low
yield (Table 2(ii), 21a: 41%). Finally, aliphatic amines such as
dipropylamine, piperidine, and morpholine were also suitable
for this reaction, giving excellent product yields (Table 2(ii),
22a–24a: 74%–97%).
Subsequently, we focused our attention on the variation of
olefins using aniline as a substrate in the presence of CO and
H2 (Table 3). Linear amines were obtained as the major pro-
ducts when styrene with various substituted groups (Table 3,
25a–27a), including electron-donating (–CH3 or –OCH3) or
electron-withdrawing (–F), were used as substrates. Especially,
the selectivity of the linear product was 99% when methyl was
substituted at the α-position of styrene, albeit in a lower yield
(Table 3, 28a: 30%). A high isolated yield of the secondary
amine could still be obtained when 1-penten, which is easily
obtained from petroleum, was used as a substrate (Table 3,
29a: 76%). Importantly, tertiary amines could be readily
obtained when small-molecule olefins such as propylene
(Table 3, 30a: 97%), ethylene (Table 3, 31a: 98%) or cyclopen-
tene (Table 3, 32a: 96%) were used as substrates.
Scheme 3 Initial reaction rates (r).
of nitrobenzene with methyl located at the meta- and ortho-
positions showed that the steric effect does exist.
Investigation of the rate-determining step
Considering the fact that a relatively higher selectivity to
amine can be obtained in the process of synthesizing 1
without observing aldehyde and imine (Fig. S4†), which are
considered to be the reaction intermediates in the literature
report,12 initial reaction rates for the three steps synthesizing 1
were then calculated to investigate the reaction route
(Scheme 3). The results showed that the initial reaction rate
(r1) for the hydroformylation of cyclohexene (step i) forming
cyclohexanecarboxaldehyde (2) was calculated to be
0.094 mmol h−1. Further condensation of 2 and aniline (step
ii) along with the hydrogenation of imine (step iii) occurred
spontaneously. Thus, the order of the initial reaction rates
demonstrates that hydroformylation of cyclohexene (step i)
forming 2 is the rate-determining step. Therefore, we conclude
that once aldehyde 2 and imine 3 are generated in steps i and
ii, they would be rapidly consumed owing to the rapid reaction
rates of steps ii and iii.
Expansion of the catalytic system
Most importantly, this catalyst system is not limited to aniline;
nitrobenzene derivatives can also be transformed to the corres-
ponding HAM products in excellent yields (Scheme 2), consid-
ering that aniline derivatives could be synthesized via hydro-
genation of nitrobenzene derivatives on the Ru/TiO2 catalyst
(Fig. S3†). Firstly, we found that the corresponding secondary
amine could be obtained in 94% yield using nitrobenzene as a
substrate in the presence of cyclohexene, CO, and H2.
Substituents can also be tolerated at the para-, meta-, and
ortho-positions of nitrobenzene, and the total yields of the
corresponding secondary and tertiary amines were obtained
up to 99%. Under the same reaction conditions, the activities
Investigation of the reactive active sites of the HAM reaction of
olefins
Reaction details of the HAM reaction of olefins were investi-
gated through in situ IR spectroscopy using dimethylamine,
ethylene, CO and H2 as the substrates, all of which were in the
gas state (Fig. 1). The mixture gas of ethylene, CO and H2 was
first introduced into the IR cell at 150 °C for 10 min and then
desorbed under vacuum (Fig. 1a). After desorption, the appear-
ance of the peaks only in the CO stretching region could be
observed. Then, excess dimethylamine gas was introduced into
the above system for 10 min and then desorbed under vacuum
(Fig. 1b). The presence of the stretching vibration of the N–H
at 3260 cm−1 for dimethylamine implied the successful intro-
duction of dimethylamine. The peak at 2137 cm−1 assigned to
Ruδ+(CO)x disappeared, indicating that Ruδ+ was the adsorp-
tion site for both CO and dimethylamine on Ru/TiO2. The
other two peaks at 2072 cm−1 and 2009 cm−1 red-shifted
owing to the strong electron-donating ability of dimethylamine
on Ru/TiO2. Therefore, we conclude that Ruδ+, existing in the
interface, is the reactive site for the HAM reaction of olefins.
Scheme 2 Synthesis of the corresponding secondary and tertiary
amines from nitrobenzene derivatives, cyclohexene, CO, and H2.
Reaction conditions: Ru/TiO2 (0.1 g), nitrobenzene derivatives
(0.2 mmol), olefin (1.0 mmol), H2 (0.5 MPa), CO (0.5 MPa), THF (2.0 mL),
160 °C, 8 h.
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Meanwhile, NH3-TPD examination (Fig. 2C) clearly showed
the higher number of acid sites of Ru/TiO2 than that in Ru/
TiO2-A and Ru/TiO2-R. The higher number of acid sites of Ru/
TiO2 is beneficial for the formation of imine via the conden-
sation reaction of amine and aldehyde (step ii).15 Besides, the
high number of acid sites of Ru/TiO2 is beneficial for the
better dispersion of Ru species on the TiO2 support, resulting
in the generation of more Ruδ+ owing to the metal–support
interaction in the interface, which is consistent with the
results from XPS characterization.14,16
Furthermore, the TEM characterizations of the three cata-
lysts are conducted to calculate the Ru particle size of the
three catalysts. The results show that the mean Ru particle
sizes were 1.8, 2.3 and 2.2 nm for Ru/TiO2, Ru/TiO2-A and Ru/
TiO2-R, respectively (Fig. 3). Obviously, the Ru particle size of
Ru/TiO2-P25 was smaller than those of Ru/TiO2-A and Ru/TiO2-
R. A high percentage of the Ruδ+ species in the premiere is pre-
sented in the smaller nanoparticle size, which contributes to
the high activity of Ru/TiO2.
Fig. 1 In situ IR spectrum for the reaction of ethylene, CO and H2 at
150 °C for 10 min, then desorbed under vacuum; (b) in situ IR spectrum
after introducing dimethylamine into (a) and then desorbed under
vacuum at 150 °C.
Discussions on the high HAM activity of Ru/TiO2
To elucidate the reasons for the high HAM activity, Ru/TiO2,
Ru/TiO2-A, and Ru/TiO2-R were characterized here because of
the different activities obtained for the HAM reaction of olefin
(Fig. 2A). The electronic state of the Ru species, which is con-
sidered one of the most important factors in various
reactions,2b,13 was further examined by X-ray photoelectron
spectroscopy (XPS). The Ru 3d5/2 peak was used for discussion
owing to the overlapping of the Ru 3d3/2 and C 1s peaks. The
higher binding energy value of Ru 3d5/2 at 280.05 eV in
Ru/TiO2 indicated the lower electron density of Ru species
(Ruδ+) in Ru/TiO2 than that in Ru/TiO2 and Ru/TiO2-R (Fig. 2B).
The lower electron density of the Ru site (Ruδ+) could improve
the desorption of generated amines, which could accelerate
the HAM reaction of olefin over the Ru/TiO2 catalyst.14
Besides, the Ruδ+ species, which acts as the active sites for CO
and cyclohexene,11 can prove the proceeding of the rate-deter-
mining step, i.e. hydroformylation of cyclohexene reaction.
Further measurement results of the specific surface area
show that the BET specific surface areas (SSAs) of the three
supports (TiO2, TiO2-A and TiO2-R) were 57.0, 83.4 and 26.1 m2
g−1, respectively. The BET specific surface areas of the three
catalysts (TiO2, TiO2-A and TiO2-R) were found to be 56.0, 68.8
and 26.0 m2 −1, respectively (Fig. 4). Obviously, the surface
g
area of TiO2-A was larger than that of the other two samples,
which is not proportional to the catalytic performance of the
three catalysts. Thus, the influence of the surface area of the
three catalysts on the catalytic performance was not necessary
for this work.
Fig. 2 Catalytic activity (A), XPS (B), and NH3-TPD (C) of Ru/TiO2,
Ru/TiO2-A, and Ru/TiO2-R. (D)Results of NH3-TPD characterization
in (C). [a] Determined by NH3-TPD expressed in micromoles of NH3
desorbed per gram of catalyst.
Fig. 3 The HRTEM of Ru/TiO2 (A), Ru/TiO2-A (B) and Ru/TiO2-R (C).
And the corresponding Ru particle size of Ru/TiO2 (D), Ru/TiO2-A (E)
and Ru/TiO2-R (F).
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TEM and HRTEM. Transmission electron microscopy (TEM)
was used to investigate the microstructures of the catalysts
using a JEOL JEM-2000EX and an FEI Tecnai G2 F30 S-Twin.
High-resolution transmission electron microscopy (HRTEM)
investigations were performed using an FEI-Titan 80–300 elec-
tron microscope equipped with a Cs corrector for the objective
lens. HAADF-STEM was performed using an FEI Titan 80–200
(ChemiSTEM). Compositional maps were obtained with
energy-dispersive X-ray spectroscopy (EDX) using four large-
solid-angle symmetrical Si drift detectors. For EDX analysis,
Ru L and Ti K peaks were used.
NH3-TPD experiments. In a typical TPD experiment, 50 mg
of the dried sample was placed in a quartz tube and pretreated
in flowing Ar at 200 °C for 1 h. Then, the temperature was
cooled to 30 °C and the sample was contacted with NH3 gas.
After NH3 adsorption, the sample was flushed with Ar (30 mL
min−1). Finally, the TPD operation was carried out by heating
the sample from 100 °C to 700 °C (10 °C min−1) under a flow
of Ar (30 mL min−1).
Fig. 4 (A) Nitrogen adsorption–desorption isotherms of TiO2, TiO2-R
and TiO2-A. (B) Nitrogen adsorption–desorption isotherms of Ru/TiO2,
Ru/TiO2-R and Ru/TiO2-A. (C) Surface area of the three supports and
three catalysts based on the calculated results in Fig. 4A and B.
XPS spectroscopy. X-ray photoelectron spectroscopy (XPS)
analysis was performed using an ESCALAB250Xi (Thermo,
USA), equipped with an Al-Kα (1486.6 eV) as the exciting
source. Spectra were collected after cooling to room tempera-
Conclusions
In summary, an efficient Ru/TiO2-catalyzed HAM reaction of ture under a high vacuum (1 × 10−8 Pa).
olefins was developed. The broad tolerance of various olefins,
including aromatic olefins, aliphatic olefins as well as various
amines, including aromatic amines, aliphatic amines, high-
lights the effectiveness of this catalytic system. The catalyst can
be recycled at least four times. Results show that hydroformyla-
tion of cyclohexene is the rate-determining step in the HAM
reaction of olefins. Moreover, nitrobenzene derivatives can
also be transformed to the corresponding HAM products in
excellent yields. This study represents an efficient route to syn-
thesize amines via the HAM reaction of olefins.
HAM reactions of olefins
HAM experiments were carried out in a 15 mL Teflon-lined
autoclave reactor. Typically, the catalyst (Ru/TiO2, 0.1 g),
aniline (0.4 mmol), solvent (THF, 2.0 mL), and a magnetic stir
bar were added into the autoclave reactor, respectively. The
reactor was purged with olefin gas (ethylene or propylene)
three times. After that, olefin gas, CO, and H2 were charged
into the reactor to a certain pressure, respectively. Finally, the
reactor was sealed and placed in a preheated mantle at 160 °C.
Further care has to be taken when we use CO and H2 owing to
their imperceptible manner. After the reaction, the autoclave
reactor was cooled with ice water. When the autoclave reactor
was cooled to room temperature, the pressure was released.
The crude reaction mixture was analyzed by gas chromato-
graphy with n-dodecane as an internal standard. The pure
product was obtained for further purification by column
chromatography on silica gel.
Experimental
Catalyst preparation
The Ru/TiO2 catalyst was prepared by the wet impregnation
method. 0.5 g of TiO2 was stirred slowly for 20 h with an
aqueous solution of RuCl3·nH2O containing 0.01 g of Ru. The
slurry was then dried at 120 °C in an oven overnight. The dried
solid sample was reduced at 350 °C for 4 h in hydrogen flow
(30 mL min−1). The content of Ru was 2.0% (wt/wt) relative to
the TiO2 support. Other catalysts such as Ru/TiO2-R, Ru/TiO2-A,
Ru/CeO2, Ru/ZnO, Ru/WO3, Ru/Al2O3, Rh/TiO2, Pd/TiO2, and
Ir/TiO2 were prepared using the same method with Ru/TiO2.
In situ IR analysis for investigating the activation site of
substrates on Ru/TiO2
In situ IR spectra were collected on a Bruker Tensor 27 instru-
ment to investigate the adsorption site of dimethylamine on
Ru/TiO2. The catalyst was pressed into a self-supporting disk
(13 mm in diameter) and placed into an IR cell. Prior to the
Catalyst characterizations
XRD characterization. X-ray powder diffraction (XRD) ana- adsorption of ethylene, CO, and H2, the sample disk was
lyses were conducted on a Rigaku D/Max 3400 powder diffrac- reduced at 350 °C for 1 h in H2 flow (30 mL min−1) and then
tion system with CuKα radiation (k = 0.1542 nm). The 2θ scans cooled to room temperature. Then, ethylene, CO, and H2 were
were taken from 10 to 80° with a step size of 0.04°. Phase introduced into the IR cell at 150 °C for 10 min and then des-
purity and crystal structures were confirmed by powder X-ray orbed by vacuum pumping for 30 min. Then, a spectrum was
diffraction profiles using the EXPGUI, GSAS package.
recorded. After that, dimethylamine was introduced into the
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IR cell at 150 °C for 10 min and then desorbed by vacuum
pumping for 30 min. Subsequently, a spectrum was recorded.
H. Neumann, F. Klasovsky, J. Pfeffer, T. Haas and M. Beller,
Angew. Chem., Int. Ed., 2011, 50, 7599–7603; (f) S. Bähn,
S. Imm, L. Neubert, M. Zhang, H. Neumann and M. Beller,
ChemCatChem, 2011, 3, 1853–1864.
Conflicts of interest
4 T. Mitsudome, K. Miyagawa, Z. Maeno, T. Mizugaki,
K. Jitsukawa, J. Yamasaki, Y. Kitagawa and K. Kaneda,
Angew. Chem., Int. Ed., 2017, 56, 9381–9385.
There are no conflicts to declare.
5 W. Reppe and H. Vetter, Justus Liebigs Ann. Chem., 1953,
582, 133–161.
6 (a) M. A. A. Seayad, H. Klein, R. Jackstell, T. Gross and
M. Beller, Science, 2002, 297, 1676; (b) M. Ahmed,
A. M. Seayad, R. Jackstell and M. Beller, J. Am. Chem. Soc.,
2003, 125, 10311–10318.
7 (a) L. Wu, I. Fleischer, R. Jackstell and M. Beller, J. Am.
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Q. Liu, R. Franke, R. Jackstell and M. Beller, Angew. Chem.,
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (22002076, 21721004, 21961130378,
U1862114), Dalian Science and Technology Innovation Fund
(2019J11CY009), the Newton Advanced Fellowships (NAF\R1
\191267).
8 J. Meng, X. H. Li and Z. Y. Han, Org. Lett., 2017, 19, 1076–
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