Supported rhodium liquid metal catalysts for the hydroformylation of olefins

Article abstract of DOI:10.1002/aoc.4555

The hydroformylation of olefins in supported room temperature liquid metals was developed, and the supported Rh liquid metal catalysts (Rh SLMCs) showed unprecedented activity and high selectivity for the hydroformylation of olefins to aldehydes. The turnover frequency is up to 7000?h^?1, much higher than that of homogeneous RhCl₃?+?3PPh₃ catalyst. Moreover, the Rh SLMCs can be recovered conveniently without obvious deactivation, and the total turnover number is up to 250?000. The active Rh(I) catalyst formed in situ can be reduced back to Rh(0) by the free electrons in liquid metal when H₂/CO gas is emitted, and thus Rh is not leaked into the organic solvent. Long-chain olefins, cycloolefins and styrenes were applied, and the corresponding aldehydes were obtained in good to excellent yields.

Full text of DOI:10.1002/aoc.4555

Received: 25 June 2018
DOI: 10.1002/aoc.4555
Revised: 20 July 2018
Accepted: 21 July 2018
F U L L P A P E R
Supported rhodium liquid metal catalysts for the
hydroformylation of olefins
Hao Sun | Wanwan Guo | Junmei Liu | Zhipeng Feng | Ruyue Li | Xuyang Zhou |
Jun Huang
State Key Laboratory of Materials‐
The hydroformylation of olefins in supported room temperature liquid metals was
developed, and the supported Rh liquid metal catalysts (Rh SLMCs) showed
unprecedented activity and high selectivity for the hydroformylation of olefins to
Oriented Chemical Engineering, College
of Chemical Engineering, Nanjing Tech
University, Nanjing 210009, People's
Republic of China
−1
aldehydes. The turnover frequency is up to 7000 h , much higher than that of
homogeneous RhCl + 3PPh catalyst. Moreover, the Rh SLMCs can be recovered
Correspondence
3
3
Jun Huang, State Key Laboratory of
Materials‐Oriented Chemical Engineering;
College of Chemical Engineering, Nanjing
Tech University, Nanjing 210009, China.
Email: junhuang@njtech.edu.cn
conveniently without obvious deactivation, and the total turnover number is up to
250 000. The active Rh(I) catalyst formed insitu can be reducedback to Rh(0) by the
free electrons in liquid metal when H /CO gas is emitted, and thus Rh is not leaked
2
into the organic solvent. Long‐chain olefins, cycloolefins and styrenes were
Funding information
applied, and the corresponding aldehydes were obtained ingood to excellent yields.
National Natural Science Foundation of
China, Grant/Award Number: 21676140;
State Key Laboratory of Materials‐
Oriented Chemical Engineering, Grant/
Award Number: ZK201711
KEYWORDS
aldehydes, hydroformylation, liquid metal, olefins, rhodium
1
| INTRODUCTION
addition, it is generally chemically stable and a series of
previous studies have proven that such an alloy is safe for
humans under normal circumstances.
[
1–3]
[9]
Room temperature liquid metals (RTLMs)
from molecular liquids and ionic liquids,
are different
and RTLMs
[4–6]
Single‐atom catalysts (SACs), with isolated atoms
behave as flowing metal cations in free electrons and reac-
tions in RTLMs are probably also different from reactions
in traditional solvents. It is interesting to study organic
reactions in RTLMs, but only few reports of dehydrogena-
tion in liquid metal at high temperature (>400°C) have
dispersed on supports, are emerging as a new frontier in
[
10–14]
the catalysis field.
the corresponding nanocatalysts
SACs are usually more active than
[
15–18]
(nanoparticles and
nanoclusters on supports) owing to the atomic dispersion.
In addition, SACs often offer high selectivity towards a spe-
cific product due to the atomic dispersion on supports. Thus,
we can consider that SACs are similar to the homogeneous
analogues but with separable properties like heterogeneous
catalysts. Recently, we reported some nanocatalysts based
on Pd, Rh and Ir for cross‐coupling reactions and reductive
amination reactions, and we are attempting to improve the
[7,8]
been published to date.
Generally, RTLMs can dissolve
catalytic active metals, and RTLMs are insoluble in organic
solvents. On the other hand, active metals in liquid metal
(metal solutions) should be atomically dispersed, and
supported metal solutions can be contacted well with reac-
tants. Gallium and gallium‐based eutectic alloys such as
GaIn (containing gallium and indium) and galinstan (con-
taining gallium, indium and tin) are liquid at room temper-
ature (or close to room temperature). The liquid metal
galinstan (GaInSn eutectic alloy made of 68.5% Ga, 21.5%
In and 10% Sn by weight) has a broad temperature range
of liquid phase with a melting point at about 10°C. In
[
19–21]
catalyst performance further.
If catalyst metals (such
as Rh, Ru or Pd) are dissolved in RTLMs, the catalyst metals
are homogeneous in liquid metals, and reactions can be
conducted in RTLMs or at the surface of the RTLMs.
Therefore the catalyst metals are atomically dispersed in
the RTLMs (metal solution), and also the catalysts can be
Appl Organometal Chem. 2018;e4555.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 9
https://doi.org/10.1002/aoc.4555

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SUN ET AL.
separated easily as the metal solution are insoluble in
organic solvents. The liquid metal catalysts are SACs also
for the corresponding reactions, and the atomic dispersion
of the catalyst metal can be maintained, which can avoid
the aggregation of the SACs. To increase the contact surface
of the catalyst metals with organic reactants, catalyst metals
in RTLMs can be dispersed on supports.
2.1.2 | Procedure for preparation of Rh
SLMCs
A typical procedure for the preparation of the catalysts
was as follows. An amount of 12 ml of a toluene solution
of rhodium acetate (Rh(Ac) ; 5.0 mg of Rh) was added
2
into galinstan liquid metal (1.0 g) in a stainless steel auto-
clave with a polytetrafluoroethylene (PTFE) liner and
with a magnetic stirring bar. After stirring for 12 h at
Rhodium‐catalyzed hydroformylation of olefins is one of
the most important industrial processes, with more than 10
million tons of aldehydes produced globally annually.
The aldehydes produced from the hydroformylation of
100°C, the reaction mixture was cooled to room tempera-
ture. Subsequently, silica (4.0 g) was added and the whole
reaction mixture was stirred at room temperature for 3 h.
The obtained precipitate was filtered and washed with
toluene, then dried under vacuum at 60°C for 6 h. This
afforded Rh‐SLMC‐0.1% (Rh‐SLMC‐0.1% catalyst con-
tains 0.1 wt% Rh and 20 wt% galinstan). Samples with
various Rh weight loading (0.5 and 0.03%) were prepared
similarly (Rh‐SLMC‐0.5% catalyst contains 0.5 wt% Rh
and 20 wt% galinstan; Rh‐SLMC‐0.03% catalyst contains
0.03 wt% Rh and 20 wt% galinstan).
[22–25]
olefins
are value‐added fine chemicals that are
employed in the synthesis of pharmaceuticals, agrochemi-
[26,27]
cals, flavorings and food additives.
But most industrial
processes use homogeneous Rh catalysts, and the catalyst
[28]
separation issue remains a problem.
Some efforts have
been devoted to develop heterogeneous catalysts for the
hydroformylation of olefins. Supported Rh nanocatalysts
were developed but with limited activity and selectivity for
[29–33]
the hydroformylation of olefins.
Besides, Rh SACs
were reported also for the hydroformylation of olefins with
[34,35]
good activity,
and the Rh SACs can be recycled easily
2
.1.3 | Preparation of Rh‐SLMC/C‐0.1%
without evident deactivation.
An amount of 12.0 ml of Rh(Ac) solution (5.0 mg of Rh)
2
In the work reported herein, the hydroformylation of
olefins in supported RTLM (galinstan) was developed,
and the supported Rh liquid metal catalysts (Rh SLMCs)
showed unprecedented activity and high selectivity for
the hydroformylation of olefins to aldehydes (Scheme 1).
Moreover, the Rh SLMCs can be recovered conveniently
without obvious deactivation. The active species, Rh(I),
formed in situ can be reduced back to metal Rh(0) by the
free electrons and dissolved into liquid metal after emitting
in toluene was added into galinstan liquid metal (1.0 g) in
a stainless steel autoclave with a PTFE liner and with a
magnetic stirring bar. After stirring for 12 h at 100°C,
the reaction mixture was cooled to room temperature.
Subsequently, activated carbon (4.0 g) was added and
the reaction mixture was stirred at room temperature
for 3 h. The obtained precipitate was filtered and washed
with toluene, then dried under vacuum at 60°C for 6 h.
The resulting catalyst is designated as Rh‐SLMC/C‐0.1%
CO/H gas, and thus no Rh leaked into the solution and the
2
(
containing 0.1 wt% Rh).
Rh SLMCs can be recovered without deactivation.
2.1.4 | Preparation of 0.1% Rh in galinstan
2
| EXPERIMENTAL
An amount of 12.0 ml of Rh(Ac) solution (1.0 mg of Rh)
2
in toluene was added into galinstan liquid metal (1.0 g) in
a stainless steel autoclave with a PTFE liner and with a
magnetic stirring bar. After stirring for 12 h at 100°C,
the reaction mixture was cooled to room temperature.
The resulting catalyst is denoted as 0.1% Rh in galinstan
2
2
.1 | Catalyst Synthesis
.1.1 | Synthesis of liquid metal galinstan
GaInSn alloy was synthesized based on a previously
[9]
reported method with a slight change. Typically, 6.7 g
of gallium, 2.05 g of indium and 1.25 g of tin metals were
added to a 100 ml Schlenk tube under argon. After the
Schlenk tube was heated at 100°C with stirring for 12 h,
the mixture was cooled to room temperature and 10.0 g
of liquid metal galinstan was obtained.
(
containing 0.1 wt% Rh).
2.1.5 | Preparation of galinstan/SiO2
An amount of 12.0 ml of toluene was added into galinstan
liquid metal (1.0 g) in a stainless steel autoclave with a
PTFE liner and with a magnetic stirring bar. After stirring
for 12 h at 100°C, the reaction mixture was cooled to room
temperature. Subsequently, silica (4.0 g) was added and the
whole reaction mixture was stirred at room temperature
SCHEME 1 SLMCs for the hydroformylation of olefins.

SUN ET AL.
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2.2 | Catalytic Hydroformylation of Olefins
The hydroformylation of olefins was conducted in a
for 3 h. The obtained precipitate was filtered and washed
with toluene, then dried under vacuum at 60°C for 6 h.
The resulting catalyst is denoted as galinstan/SiO2.
30.0 ml stainless steel autoclave equipped with a stirring
bar. In a typical procedure, 5.0 mmol of styrene,
−
5
1
0.0 mg of Rh‐SLMCs‐0.1% (about 10 mmol Rh metal)
2
.1.6 | Preparation of the 0.1%Rh/SiO2
and 4.0 ml of toluene were added into the autoclave.
Then, the autoclave was flushed five times with 1.0 MPa
H , and charged successively with 2.0 MPa H and 2.0
2 2
MPa CO gas. After the autoclave was sealed, it was
heated to 100°C in an oil bath for 8 h. After reaction,
0.3 ml of n‐hexadecane was added as the standard. The
products were qualitatively analyzed using GC‐MS.
Products were quantitatively analyzed using an Agilent
7890A gas chromatograph equipped with an HP‐5
capillary column and flame ionization detector.
Silica (1.0 g) was dispersed into 15.0 ml of ethanol and the
suspension was stirred at room temperature for 15 min.
Then, 5 ml of RhCl ⋅3H O solution (1.0 mg of Rh) in
ethanol was added dropwise (1.0 ml min ) to the
suspension. The resulting slurry was stirred for 3 h and
ethanol was removed slowly under vacuum. The remain-
ing solid sample obtained was dried at 60°C for 12 h. The
3
2
−
1
dried sample was reduced using H at 200°C for 3 h,
affording 0.1%Rh/SiO (containing 0.1 wt% Rh).
2
2
FIGURE 1 Preparation of Rh SLMCs: (a) galinstan liquid metal with toluene; (b) galinstan liquid metal with toluene solution of rhodium
acetate; (c) Rh metal in galinstan solution dispersed in toluene; (d) Rh metal solution under toluene after centrifugation at 6000 rpm.
FIGURE 2 SEM images of Rh‐SLMC‐0.1: (a) Rh‐SLMC‐0.1%, scale bar = 100 μm; (b) Rh‐SLMC‐0.1%, scale bar = 1 μm; (c) recycled Rh‐
SLMC‐0.1%, scale bar = 100 μm; (d) recycled Rh‐SLMC‐0.1%, scale bar = 1 μm.

4
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SUN ET AL.
The catalyst Rh‐SLMCs‐0.1% was separated by
the toluene by centrifugation (Figure 1d). The Rh SLMCs
can be obtained by dispersion of the Rh liquid metal
solution on silica.
filtration and washed with n‐hexane. The recovered Rh‐
SLMCs‐0.1% was used again for a subsequent reaction
under the same conditions.
3.2 | Characterization of Catalysts
2.3 | Catalyst Characterization
The Rh SLMCs were characterized using SEM. Figure 2
shows SEM images of Rh‐SLMC‐0.1%. The Rh solution
in galinstan liquid metal was dispersed well on the silica
(Figure 2a,b), and small spheres of about 100 nm of the
liquid metal phase were found on the surface of silica.
Moreover, the appearance of the recycled Rh‐SLMC‐
0.1% catalyst was similar to that of the fresh catalyst,
and the liquid metal phase was also dispersed as small
spheres of about 100–200 nm on the silica (Figure 2c,d).
A small liquid sphere was analyzed using SEM/energy‐
dispersive X‐ray spectroscopy, and the amount of Rh
was about 0.05 at% and 0.26 wt%, which is in agreement
with the Rh liquid metal solution. In addition, Ga, In
and Sn were found in the liquid metal sphere. And no
X‐ray photoelectron spectroscopy (XPS) data were
obtained with an ESCALab220i‐XL electron spectrometer
from VG Scientific using 300 W Al Ka radiation. X‐ray dif-
fraction (XRD) patterns were collected with a Bruker D8
Advance powder diffractometer using Ni‐filtered Cu Kα
radiation source at 40 kV and 20 mA, from 5° to 95° with
−
1
a scan rate of 0.5° min . The base pressure was about
−
9
3
× 10 mbar. Scanning electron microscopy (SEM)
images were obtained with a Hitachi S‐4800 field‐emission
scanning electron microscope. Brunauer–Emmett–Teller
(BET) surface areas were measured at the temperature of
liquid nitrogen using a Micromeritics ASAP2010 analyzer.
The samples were degassed at 150°C to a vacuum of
−
3
1
0
Torr before analysis. The amount of Rh was measured
using a Jarrell‐Ash 1100 inductively coupled plasma
atomic emission spectrometry (ICP‐AES) instrument.
3
3
| RESULTS AND DISCUSSION
.1 | Analysis of Preparation Process of
Rh SLMCs
The Rh SLMCs were prepared by supporting the Rh
galinstan liquid metal solution on supports. Rh(Ac) solu-
2
tion in toluene was added into the galinstan liquid metal
in a stainless steel autoclave with a PTFE liner and mag-
netic stirring bar. When the reaction mixture was heated,
Rh(Ac) was reduced to Rh metal by Ga metal (excess Ga
2
added), and then Rh metal was dissolved into galinstan
liquid metal. So Rh in galinstan liquid metal solution
was obtained. Silica was added into the mixture of the
liquid metal solution and toluene with stirring, and then
the Rh SLMCs were obtained after removal of the toluene
by filtration. The process of the preparation of the Rh
SLMCs is shown in Figure 1. The galinstan liquid metal
with toluene is shown in Figure 1(a), with the galinstan
liquid metal layer being under the toluene layer. When
rhodium acetate was dissolved in the upper toluene layer,
we can see the green rhodium acetate toluene solution on
the galinstan liquid metal layer (Figure 1b). When the
galinstan liquid metal with rhodium acetate toluene solu-
tion was heated, the rhodium acetate was reduced to Rh
metal and dissolved in galinstan liquid metal. The Rh
metal solution in galinstan liquid metal can be dispersed
in toluene (Figure 1c). And then the Rh metal solution in
galinstan liquid metal can be obtained after separation of
2
FIGURE 3 (a) N adsorption/desorption isotherm and pore size
distribution of silica; (b) N adsorption/desorption isotherm and
2
pore size distribution of Rh‐SLMC‐0.1%.

SUN ET AL.
5 of 9
Rh was found in the silica surface without liquid metal
sphere (supporting information, Figure S1).
the hydroformylation of styrene (Table 1, entries 1–3).
Similar catalyst Rh‐SLMC/C‐0.1% with activated carbon
as support was not as good due to the poor wettability
of the galinstan with activated carbon, as some liquid
metal was left out beside the supported Rh‐SLMC/C‐
Nitrogen adsorption/desorption analysis showed
typical type IV isotherms for Rh‐SLMC‐0.1% and silica
gel (Figure 3). The BET specific surface of Rh‐SLMC‐
2
−1
0
.1% is about 235 m g with an average pore diameter
of 9.4 nm, which is slightly decreased from the parent
2
−1
silica gel (307 m g with pore diameter of 9.6 nm). Rh
is present in the Rh‐SLMC‐0.1% catalyst as both Rh(0)
3+
and Rh states as determined from XPS spectra, although
the signals are not strong. But the recycled Rh‐SLMC‐0.1%
catalyst contained mainly Rh(0) (Figure 4). From the XRD
patterns of silica and Rh‐SLMC‐0.1%, we can see a new
weak peak of Ga O3 formed possibly by the partial
2
oxidation of Ga with air (Figure 5).
3
.3 | Catalytic Performance of Rh SLMCs
for Hydroformylation of Olefins
The hydroformylation of styrene was studied as a model
reaction for the optimization of reaction conditions.
Firstly, the amount of Rh in the Rh‐SLMC catalysts was
studied, and Rh‐SLMC‐0.1% was found to be good for
FIGURE 5 XRD patterns of Rh‐SLMC‐0.1% and silica.
0
3+ [34,35]
FIGURE 4 XPS spectra of Rh: (a) fresh Rh‐SLMC‐0.1% catalyst; Rh 3d: 307 eV and 313.4 eV are Rh ; 309.1 eV and 314.8 eV are Rh
;
0
3+ [34,35]
(
b) recycled Rh‐SLMC‐0.1% catalyst; Rh 3d: 306.7 eV and 311.5 eV are Rh ; 308.8 eV is Rh
;
(c) fresh Rh‐SLMC‐0.1% catalyst; Ga 3d:
(d) recycled Rh‐SLMC‐0.1% catalyst; Ga 3d: 18.6 eV is Ga ; 20.6 eV is Ga ; 25.0 eV is
0
3+
[36]
0
3+
1
8.3 eV is Ga ; 20.3 eV is Ga ; 25.0 eV is O 2s signal;
[36]
O 2s signal.

6
of 9
SUN ET AL.
a
TABLE 1 Hydroformylation of styrene with various catalysts
b
c
d
−1 e
Entry Catalyst
l:b S (%) Y (%) TOF (h )
1
2
3
4
5
6
7
8
9
Rh‐SLMC‐0.5%
1.1 99
1.1 99
1.1 99
1.1 99
1.0 83
1.0 94
1.0 99
56
99
90
19
9
3601
6367
5788
1222
579
Rh‐SLMC‐0.1%
Rh‐SLMC‐0.03%
Rh‐SLMC/C‐0.1%
RhCl
RhCl
3
3
+ 3PPh
3
37
31
29
0
2380
1994
1865
0
0.1%Rh/SiO
2
0.1% Rh in galinstan 1.1 99
Galinstan/SiO 0
2
—
a
Reaction conditions: 5.0 mmol of styrene; styrene/Rh = 51450 (mol/mol);
4
2
.0 ml of toluene; 2.0 MPa H , 2.0 MPa CO; at 100°C; for 8 h.
FIGURE 6 Hydroformylation of styrene as a function of reaction
time. Reaction conditions: 5.0 mmol of styrene; styrene/Rh = 51450
b
l:b = linear:branch.
c
Selectivity.
(
2
mol/mol); 4.0 ml of toluene; 2.0 MPa H , 2.0 MPa CO; at 100°C.
d
Yields determined by GC.
e
TOF (turnover frequency) denotes moles of aldehyde (l + b) produced per
mole of Rh catalyst per hour.
corresponding aldehydes (l + b) smoothly with good
selectivity. The selectivity to aldehydes (l + b) was kept
high from the start to the end (complete conversion).
And the reaction rate was stable in the first 6 h (at about
90% conversion), and then went slightly down in the last
2 h (from 90to 100% conversion).
0
.1% catalyst after dispersion of Rh liquid metal solution
on activated carbon (Table 1, entry 4). Additionally,
RhCl only and homogeneous RhCl with PPh catalysts
3
3
3
were found to be of low selectivity and low activity for
the hydroformylation (Table 1, entries 5 and 6). The
With the optimized reaction conditions in hand, the
application scope of the Rh‐SLMC‐0.1% catalyst was inves-
tigated for the hydroformylation and the results are listed
in Table 3. The hydroformylation of 4‐chlorostyrene gave
the corresponding aldehydes in 99% yield, and the TOF
0
.1% Rh/SiO2 without galinstan and the Rh solution
(0.1% Rh in galinstan) without support are not as active
as the Rh‐SLMC‐0.1% catalyst (Table 1, entries 7 and 8).
Also, galinstan/SiO without Rh was completely inactive
2
−
1
(Table 1, entry 9). Although recently Rh SACs have been
was up to 7004 h (Table 3, entry 2), which is much
found to be highly active for hydroformylation, the turn-
higher than that with homogeneous RhCl + 3PPh3
3
−
1
over frequency (TOF) of Rh‐SLMC‐0.1% catalyst is up to
catalyst (2500 h ). Moreover, the selectivity of homoge-
neous RhCl + 3PPh catalyst for the hydroformylation
−
1
6
367 h , which is much higher than that of SACs and
3
3
homogeneous Rh catalysts (Table 2, summary of recently
reported results).
Next, the process of the hydroformylation of styrene
catalyzed by Rh‐SLMC‐0.1% based on reaction time was
studied (Figure 6). Styrene was converted to the
of styrene (94% to aldehydes, 6% to ethyl benzene) and 4‐
chlorostyrene (92% to aldehydes, 8% to ethyl benzene)
was lower than that of the Rh‐SLMC‐0.1% catalyst
(Table 3, entries
1
and 2). Additionally, the
hydroformylation of cyclopentene and cyclohexene gave
the corresponding aldehydes in good yields in 18 h
(
Table 3, entries 3 and 4). But the hydroformylation of
TABLE 2 Representative Rh nanoparticle‐catalyzed
hydroformylation of styrene
cyclooctene gave cyclooctanecarbaldehyde in 82% yield
even at lower substrate‐to‐catalyst ratio (Table 3, entry
5
dodecene, were converted to the corresponding
aldehydes in good yields at high TOFs (Table 3, entries
5–8). Moreover, the hydroformylation of 3‐hydroxy‐2‐
methylpropene was studied, with 4‐hydroxy‐3‐
methylbutanal being obtained in good yield (Table 3, entry
Selectivity TOF
). Aliphatic olefins, such as n‐hexene, n‐octylene and n‐
−1
Entry Catalyst
l:b (%)
(h
)
Ref.
1
2
Rh‐SLMC‐0.1% 1.1 99
6367
3333
This work
[35]
a
0.006%Rh/
1.0 99
ZnO‐nw
a
a
a
[31]
[32]
[33]
3
5
6
Rh/ZIF‐8
0.4 99
0.2 99
0.5 99
42
239
9
3
). Also, the hydroformylation of 2‐phenyl‐1‐propene gave
‐phenylbutanal in 80% yield (Table 3, entry 10). From
Rh‐PPh
Rh/Al
3 2
/SiO
2
O
3
3200
these results, most of the olefins can be converted to the
corresponding aldehydes with excellent selectivity.
a
Reported TOF value.

SUN ET AL.
7 of 9
a
TABLE 3 Rh‐SLMC‐0.1%‐catalyzed hydroformylation of various olefins
b
c
d
e
−1 f
Entry
Product
S:C
Time (h)
l:b
C (%)
S (%, l + b)
TOF (h
)
1
51450
8
1.1
1.0
100
99
6367
(2380)
h
h
(
94)
2
56595
8
100
99
7004
(2500)
h
h
(
92)
3
4
51450
51450
18
18
/
/
99
98
99
99
2801
2773
5
5145
18
/
83
98
232
6
51450
51450
12862
5145
8
1.0
1.0
1.2
>99
100
98
98
98
98
98
6303
4941
1029
232
g
7
10
12
18
8
9
98
83
1
0
12862
12
>99
81
99
859
a
Reaction conditions: 4.0 ml of toluene; 2.0 MPa H
2
; 2.0 MPa CO; at 100°C.
b
S:C = substrate (mol):catalyst (Rh mol).
c
l:b = linear:branch.
d
Conversions determined by GC.
Selectivity.
e
f
TOF (turnover frequency) denotes moles of aldehyde produced per mole of Rh catalyst per hour.
g
4.0 ml of n‐hexane as solvent.
h
3 3
Homogeneous catalyst (RhCl + 3PPh ) was used.
3.4 | Reusability of Catalyst Rh‐SLMC‐0.1%
The reusability of Rh‐SLMC‐0.1% was tested for the
hydroformylation of styrene and the results are shown
in Figure 7. Rh‐SLMC‐0.1% can be reused at least five
times without obvious loss of reactivity. The slight
deactivation of the Rh‐SLMC‐0.1% catalyst may be due
to the loss of the catalyst in the recycling processes. The
total turnover number (TON) is up to 250 000, which is
unprecedentedly high compared to similar catalysts.
Moreover, no Rh was detected (ICP‐AES) in the solution
after removal of the catalyst by filtration.
3
.5 | Proposed Mechanism of
Hydroformylation of Olefins over Rh
SLMCs
FIGURE 7 Recycling experiment for Rh‐SLMC‐0.1%. Reaction
The mechanism of the Rh‐SLMC‐0.1%‐catalyzed
conditions: 5.0 mmol of styrene; styrene/Rh = 51450 (mol/mol);
hydrformylation of styrene was studied, and some control
2
4.0 ml of toluene; 2.0 MPa H , 2.0 MPa CO; at 100°C; for 8 h.

8
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SUN ET AL.
FIGURE 8 Proposed mechanism of hydroformylation of olefins over Rh SLMCs.
experiments were conducted. When hydrogenation of
styrene (the reaction without CO gas, under 2.0 MPa
H2) was conducted (same reaction conditions as
Table 1, entry 2, but without CO), the conversion of
styrene to ethylbenzene was only about 2% (supporting
information, Table S1, entry 1). The result implied that
the Rh‐SLMC‐0.1% catalyst was firstly activated by CO
gas, and the hydrogenation byproduct, ethylbenzene,
was low. Moreover, the recycled Rh‐SLMC‐0.1% catalyst
was found mainly to be Rh(0) metal state from XPS
spectra (Figure 4). The active Rh(I) was reduced back
to Rh(0) metal by free electrons and dissolved in liquid
hydroformylation of olefins to aldehydes. The TOF is up
to 7000 h , much higher than that of homogeneous
−
1
RhCl + 3PPh catalyst and SACs. Long‐chain olefins,
3
3
cyclo‐olefins and styrenes were applied, and the corre-
sponding aldehydes were obtained in good to excellent
yields. Moreover, the Rh SLMCs can be recovered conve-
niently without obvious deactivation, and the total TON
is up to 250 000. The active species, Rh(I), formed in situ
can be reduced back to metal Rh(0) by free electrons and
dissolved into liquid metal after emitting CO/H gas, and
2
thus no Rh leaked into the solution and the Rh SLMCs
can be recovered without deactivation. We believe more
organic reactions in liquid metals will be developed, and
more insights can be obtained in the near future.
metal when the CO/H gas was given out, since the
2
active Rh center should be Rh(I) and liquid metal has
free electrons. As the liquid metal phase is not soluble
in toluene, the Rh‐SLMC‐0.1% catalyst can be recovered
without Rh loss. A possible mechanism is presented
ACKNOWLEDGMENTS
(
Figure 8).
This work was supported by the National Natural Science
Foundation of China (grant no. 21676140) and the fund
from the State Key Laboratory of Materials‐Oriented
Chemical Engineering (grant ZK201711).
4
| CONCLUSIONS
In summary, we developed the hydroformylation of ole-
fins in supported RTLM (galinstan) firstly, and the Rh
SLMCs showed high activity and high selectivity for the
ORCID
Jun Huang http://orcid.org/0000-0001-6797-377X

SUN ET AL.
9 of 9
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How to cite this article: Sun H, Guo W, Liu J,
et al. Supported rhodium liquid metal catalysts for
the hydroformylation of olefins. Appl Organometal
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