Magnetic nanoparticle supported triphenylphosphine ligand for the Rh-catalyzed hydroformylation reaction

Article abstract of DOI:10.1016/j.catcom.2014.01.012

A magnetic recyclable nano-triphenylphosphine (nano-TPP) ligand was synthesized by simply loading a dopamine-triphenylphosphine derivative onto the surface of super paramagnetic iron oxide nanoparticle (SPION). Via the cooperation between surface neighbor TPP units, nano-TPPs can bond to Rh atoms forming magnetic recyclable nano-TPPRh complexes to catalyze the hydroformylation reaction and can be reused for 20 times with the compensation of Rh salt.

Full text of DOI:10.1016/j.catcom.2014.01.012

Catalysis Communications 48 (2014) 45–49
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Magnetic nanoparticle supported triphenylphosphine ligand for the
Rh-catalyzed hydroformylation reaction
a,b,
a
a
a
a
b
Chuansong Duanmu ⁎, Linlin Wu , Jian Gu , Xingyou Xu , Liangdong Feng , Xu Gu
a
College of Life Sciences and Chemical Engineering, Huaiyin Institute of Technology, Huaian, Jiangsu Province 223003, PR China
Jiangsu Provincial Engineering Laboratory of Advanced Materials for Salt Chemical Industry, Huaiyin Institute of Technology, Huaian, Jiangsu Province 223003, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A magnetic recyclable nano-triphenylphosphine (nano-TPP) ligand was synthesized by simply loading a
dopamine-triphenylphosphine derivative onto the surface of super paramagnetic iron oxide nanoparticle
Received 5 November 2013
Received in revised form 11 January 2014
Accepted 13 January 2014
Available online 29 January 2014
(
SPION). Via the cooperation between surface neighbor TPP units, nano-TPPs can bond to Rh atoms forming
magnetic recyclable nano-TPPRh complexes to catalyze the hydroformylation reaction and can be reused for
0 times with the compensation of Rh salt.
2
©
2014 Elsevier B.V. All rights reserved.
Keywords:
Hydroformylation
Magnetic recyclable nano-triphenylphosphine
Surface cooperation
1
. Introduction
As one of the largest volume processes, hydroformylation catalysis
2. Experimental
2.1. Chemical reagents and instrumentation
has been well established in the chemical industry relying on homoge-
neous catalysts. However, catalyst separation still remains a paramount
challenge and retains a lot of research attention. To overcome this limi-
tation, many approaches have been explored, which could be roughly
grouped into two strategies. One is based on biphasic or multiphasic
Most chemicals were purchased from Acros and J&K Chemicals and
used as received. Anhydrous tetrahydrofuran (THF) was obtained
from the distillation over CaH under N atmosphere. H and CO gases
2 2 2
with purity of 99.9% were bought from Zhongxin Industrial Gas Service
Co. (Huaian, China).
2
catalytic system using aqueous biphase [1,2], supercritical CO [3],
ionic liquids [4], or gas-expanded liquids [5] as reaction mediums. The
other is the heterogenization of homogeneous catalysts by anchoring
them onto different supports, such as polymers [6–8], supported ionic
liquid phase [9,10], silica [11], alumina [12] or other oxides [13]. In the
past decade, the breakthrough in the large-scale synthesis of super
paramagnetic iron oxide nanoparticles (SPIONs) [14] offered us a new
platform to develop semi-homogeneous magnetic recyclable catalysts
by fixing homogeneous catalytic species onto nanoparticle surfaces
1H NMR data were obtained on a Bruker AVANCE AV 400 MHz sys-
tem and the chemical shifts were reported in parts per million (ppm)
downfield relative to tetramethylsilane (TMS). TEM measurements
were accomplished with a Philips Tecnai G2 F30 S-TWIN operating at
an accelerating voltage of 100 kV and SPIONs were deposited on
carbon-coated 400 mesh copper grids (Beijing Zhongjingkeyi Technolo-
gy Co., Ltd). Gas chromatography analyses were carried on Agilent 6820
with flame ionization detector (FID). Elemental analyses were per-
formed on Elementar Vario EL III. Rhodium contents in recycled cata-
lysts were determined by the ICP-OES method on Perkin-Elmer
Optima 7000DV.
[15]. But the difficulties in the surface functionalization of iron oxide
nanoparticles limited their application as magnetic catalyst supports
in the hydroformylation process [16]. Herein, we report a simple
method to prepare a magnetic recyclable nano-triphenylphosphine
ligand (nano-TPP) for hydroformylation catalysis by anchoring TPP
ligands onto the surfaces of SPIONs through dopamine linkers.
2.2. Synthesis of magnetic nano-triphenylphosphine ligand
(
nano-TPP) (Scheme 1)
2.2.1. Synthesis of dopamine-triphenylphosphine derivative (D-TPP)
4
-(Diphenylphosphino)benzoic acid (100.6 mg), dopamine
hydrochloride (74.3 mg), 1-hydroxybenzotriazole (HOBt, 52.7 mg), 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC, 74.8 mg) and
triethylamine (TEA, 54 μL) were mixed in 6 mL N,N-dimethylformamide
⁎
Corresponding author. Tel.: +086 15152357615.
E-mail address: CDuanmu@126.com (C. Duanmu).
1566-7367/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2014.01.012

46
C. Duanmu et al. / Catalysis Communications 48 (2014) 45–49
Scheme 1. Synthesis of magnetic nano-TPP ligand.
(
1
DMF) under Ar atmosphere and stirred overnight at room temperature.
5 mL water and 5 mL ethyl acetate were then added to the reaction mix-
2.2.3. Preparation of nano-TPP ligand
3
SPIONs (98.4 mg, in 3.5 mL CHCl ) were mixed with a D-TPP solution
ture and 1 M HCl was applied to adjust the pH to about 3.5. The organic
layer was collected and the removal of solvent gave the crude product.
The white solid pure D-TPP (133.4 mg, yield 92.0%) was obtained via
flash chromatography purification (ethyl acetate/n-hexane: 1:5). IR
(103.8 mg in 6.0 mL DMF) and sonicated for 6 h at room temperature
under argon. The magnetic nano-TPP ligands were then collected by a
magnet, rinsed by anhydrous THF for 3 times and kept in 10 mL
anhydrous THF.
−
1
(
(
KBr): ṽ (cm ) 3396 (phenol), 3005 (phenyl), 2921 (CH
CH ), 1690 (carbonyl), 694 (phenyl), 634 (phenyl), 590 (phenyl). H
) δ 2.63 (t, 2H, CH ), 3.50 (q, 2H, CH ), 5.26 (s,
H, OH), 6.46 (d, 1H, Ar), 6.60 (t, 1H, Ar), 6.69 (s, 1H, Ar), 6.72 (d, 1H,
Ar), 7.25 (m, 11H, Ar), 7.53 (q, 2H, Ar). MS (ESI): calcd for C27 24NO P:
2
), 2851
1
2
NMR (400 MHz, CDCl
2
3
2
2
2.3. Typical procedure for styrene hydroformylation of and catalyst
recycle (Scheme 2)
H
3
+
441.2; found: 442.1 ([M + H] ).
1.25 mL styrene (10.9 mmol), 30 mg magnetic nano-TPP (in 3.0 mL
THF, 0.0064 mmol TPP), 1.8 mg Rh(OAc)
hydrous THF were added to a stainless high pressure reactor (equipped
with a 100 mL Teflon inner tank). The reactor was flushed by CO and H
gas for 3 times each, and then pressurized to 3 MPa by synthesis gas (CO
and H , 1:1). The reactor was then sealed well and heated in an oil bath
at 90 °C with magnetic stirring. The reaction mixture was cooled down
to the room temperature after 9 h, and poured into a glass bottle
attached with a magnet outside. After all nano-TPP–Rh complexes
were collected onto the inside wall of the glass bottle, the reaction
2
(0.0081 mmol) and 12 mL an-
2
.2.2. SPION synthesis and pretreatment
2
The SPIONs were synthesized according to Hyeon's procedure
14]. The obtained crude oily product solution (3 mL, as an example)
was then washed sequentially by 95% ethanol (6 mL × 4) and CHCl
CH CN (3 mL/1 mL × 4) to remove 1-octadecene and extra oleic acid
[
2
3
/
3
to give the final ready-to-use SPIONs (~10 nm in diameter), which
were stored in 2 mL chloroform (28.1 mg/mL).
Scheme 2. Hydroformylation of styrene and proposed structure of magnetic recyclable nano-TPP–Rh complex formed during the reaction.

C. Duanmu et al. / Catalysis Communications 48 (2014) 45–49
47
Fig. 1. TEM image of SPIONs (a), photos of nano-TPP in THF (b) and nano-TPP–Rh complex collection from the hydroformylation reaction media by magnets (c).
solution was transferred to another bottle to store for production puri-
fication and yield determination. The collected nano-TPP–Rh complexes
were then rinsed with anhydrous THF for 3 times and charged into the
pressure reactor to catalyze the next round of hydroformylation
The amount of TPP ligands on SPIONs was calculated from the
elemental analysis data of nitrogen, which was the element only
present in D-TPP. The elemental analysis results and TPP-loading
amounts in nano-TPPs prepared under different ligand-exchange condi-
tions are listed in Table 1, which indicated that the higher D-TPP/SPION
ratio and longer sonication time generally yielded more TPP loading. Fi-
nally 2.4 μmol/mg D-TPP/SPIONs and 6-hour sonication were picked up
as the preparation condition for the nano-TPP ligand, in which the TPP
content was 0.214 μmol/mg. The good solubility of the nano-TPP in
THF (Fig. 1b) makes it possible to act as a homogeneous catalyst by
coordinating with a catalytic metal.
2
reaction without any more addition of Rh(OAc) as a precatalyst. The
aldehyde yield and n/i ratio were determined by a GC method.
3
. Results and discussion
3
.1. Preparation and characterization of magnetic nano-TPPs
The TEM image of SPIONs is shown in Fig. 1a and their average
diameter is 10 nm. The crude SPIONs prepared via Hyeon's process
were covered by a lot of oleic acid hindering the further loading of
catalytic species onto their surfaces. Thus a simple washing process
3.2. Catalytic testing
This novel nano-TPP ligand showed high catalytic activity and
magnetic recyclability in the hydroformylation of styrene. In our initial
investigation, the reaction was run at 150 °C (oil bath temperature) in
3 3
was developed using CHCl /CH CN (v/v = 3) mix-solvent to remove
extra oleic acid and some amorphous iron oxide particles by the way.
The D-TPP was designed to anchor triphenylphosphine ligand onto
the SPION surface via the chelation of two phenol groups in dopamine
unit with the surface iron atom of SPION [17], which could offer a stable
binding under various conditions [18,19].
3
the presence of RhCl as the precursor in THF, which was considered
as a good solvent favoring the desired hydroformylation over hydroge-
nation of olefins [20]. The reaction proceeded well and the yield reached
82.2% in 4 h (Table 2, entry 1). However the recycled SPIONs did not
Table 1
TPP contents in nano-TPPs prepared under different conditions.
Entry
Sample ID
N%
TPP contenta (μmol/mg)
Prep. cond.
D-TPP/SPION (μmol/mg)
Sonication time (h)
1
2
3
4
SPION
0
0
Nano-TPP-1
Nano-TPP-2
Nano-TPP-3
0.13
0.30
0.40
0.093
0.214
0.286
1.2
2.4
4.8
3
6
6
a
TPP content in dry nano-TPP samples determined by the elemental analysis method.
Table 2
Optimization of styrene hydroformylation condition.
Entry
Rh salt
Syngas initial pressure (MPa)a
Oil bath temp. (°C)
Reaction time (h)
Yield (%)
n/i
Round #
1
1
2
3
4
5
6
7
RhCl
3
2.0
2.0
2.0
2.0
2.0
3.0
3.0
150
150
120
90
90
90
4
20
20
20
20
9
82.2
n/a
29.1
n/a
1.66
n/a
0.34
n/a
0.29
0.66
0.64
b
2
RhCl
RhCl
3
1
1
1
1
1
3
Rh(OAc)
Rh(OAc)
Rh(OAc)
2
55.3
93.9
2
c
2
90
9
52.1
a
CO/H
2
1:1 and nano-TPP was 30 mg containing 6.4 μmol TPP ligands in each reaction.
No extra RhCl was added in the second round hydroformylation reaction.
The reaction was run in the absence of nano-TPP.
b
c
3

48
C. Duanmu et al. / Catalysis Communications 48 (2014) 45–49
Table 3
Nano-TPP–Rh complex recycle and catalytic performance of hydroformylation.
Entry
Round #
Yielda (%)
n/ia
TPP content
μmol/mg)
TON
Rh Content in SPIONsb
(μmol/mg)
Rh left in reaction liquidc
(μmol)
(
1
2
3
4
5
6
7
8
1d
2
1
2
3
4
5
20
98.9
n/a
0.41
n/a
0.093
0.093
0.214
0.214
n/a
e
94.3 (91.4)
94.9 (90.7)
77.3 (70.2)
76.3 (68.5)
43.7
0.54
0.55
0.45
0.61
0.63
0.61
7.23
0.09
n/af
13,261
12,766
13,201
12,213
0.026
0.022
0.021
0.013
0.21
g
40.1
0.186
a
Yield and n/i ratio were determined by the GC method.
Rh content in dry nano-TPP–Rh complex was determined before the hydroformylation reaction by ICP-OES method.
The total amount of Rh left in the reaction liquid after reaction and removal of nano-TPP–Rh complexes by a magnet.
b
c
d
Each round of hydroformylation was run under the same condition: 10.9 mmol styrene, 30 mg nano-TPP (in 3 mL THF), 1.8 mg Rh(OAc)
2
(added every 5 rounds of reactions), syngas
pressure 3 MPa, 12 mL THF, oil bath temperature 90 °C, reaction time 9 h.
e
The numbers in parentheses were isolation yields obtained via flash column chromatography.
The Rh content in reaction liquid was too low to be measured by the ICP-OES method.
f
g
2
1.8 mg Rh(OAc) was compensated every 5 rounds of hydroformylation.
show any catalytic activity in the next round of hydroformylation with-
out the compensation of RhCl (Table 2, entry 2), indicating no enough
7). In our tests, the aldehyde yield of styrene was still 43.7% after four
recycles of nano-TPP–Rh catalytic complexes (Table 3, entry 7). Consid-
ering the almost unchanged TPP contents in the recycled nano-TPP–Rh
complexes, the loss of their catalytic activity was mainly attributed to
the decomposition of nano-TPP–Rh complexes causing the leaching of
Rh atoms from SPION surfaces, which was also confirmed by the Rh
content measurements (Table 3, entries 3 to 7). With the compensation
of Rh salt (one time per five reaction cycles), nano-TPP could be
reactivated and used for 20 reaction cycles (Table 3, entry 8). The n/i
ratios in this recyclable catalysis system were only around 0.5 lower
than industrialized catalytic systems [21], which may be due to the
nano-surface environment on SPIONs, because the iso-aldehyde
preference was also found in other Rh-catalyzed hydroformylations
in nano-environmental catalytic systems [22,23].
3
active dopamine-triphenylphosphine–Rh complexes left on SPIONs
after the high-temperature reaction. It maybe caused by the drop-off
of D-TPP from the SPION surface, which was supported by the elemental
analysis result. After the reaction the nitrogen content in the recycled
SPIONs became undetectable. Thus, lower temperatures (120 °C and
9
0 °C) were selected in the following hydroformylation tests. The reac-
tion rate slowed down significantly at 120 °C and even stopped at 90 °C
in the first round of reaction (Table 2, entries 3 and 4), which may be
due to the poor solubility of RhCl
3
in THF at lower temperature.
Rh(OAc) was then tried as a catalyst precursor because of its better
2
solubility in THF and the hydroformylation reaction could be finished
in 20 h at 90 °C (Table 2, entry 5). When the initial syngas pressure
was lifted to 3.0 MPa (CO and H
much faster and finished in 9 h (Table 2, entry 6).
During the hydroformylation, Rh(OAc) and surface TPP ligands
could form catalytic complexes (nano-TPP–Rh complexes) on the
SPION surfaces, which exhibited much higher catalytic activity than
2
, 1:1), the reaction was accelerated
The recyclability to Rh atoms was greatly affected by the D-TPP
concentration on the SPION surface. Too low D-TPP concentration
(0.093 μmol/mg, Table 3, entries 1 and 2) caused no detectable Rh
atoms left in collected SPIONs after hydroformylation, which suggested
that the Rh atom did not form a stable enough bond with single D-TPP
ligand to be kept on the SPION surface. This concentration dependent
recyclability of nano-TPP–Rh complexes indicated that the two
neighbor D-TPP units cooperated with each other to bond to one
Rh atom simultaneously to form a stable complex as chelation bond-
ing (Scheme 2) [24]. This interesting type of cooperation between
surface ligands on nanoparticles was also found in our previous
research [18]. To improve the nano-TPP–Rh recyclability, further
2
2
Rh(OAc) (Table 2, entries 6 and 7). The in situ formed nano-TPP–Rh
complexes were magnetically collectable with SPIONs together from
the reaction mixture (Fig. 1c) and could keep their high catalytic activity
indicating the formation of stable binding between TPP ligands and Rh
atoms. The TON of the recycled nano-TPP–Rh complex was higher
than 13,000 in the 2nd round of hydroformylation reaction and did
not drop down much in the following recycles (Table 3, entries 4 to
Table 4
a
Scope and limitation of nano-TPP–Rh catalyzed hydroformylations.
Entry
Olefin
Product
Yieldb (%)
n/i ratiob
n-Aldehyde
i-Aldehyde
1
2
95.8
94.2
0.90
1.00
1.45
3
4
77.4
No reaction
No reaction
5
a
2
Each reaction was run under the same condition: 10.9 mmol olefin, 30 mg nano-TPP (in 3 mL THF), 1.8 mg Rh(OAc) (added in 1st catalytic run), syngas pressure 3 MPa, 12 mL THF, oil
bath temperature 90 °C, reaction time 9 h.
b
The yield and n/i ratio were obtained from the 2nd catalytic run by the GC method.

C. Duanmu et al. / Catalysis Communications 48 (2014) 45–49
49
studies to increase the D-TPP concentration on SPION surfaces are in
progress.
Some other olefins were also tested to evaluate the application scope
and limitation of the nano-TPP–Rh catalytic system. The results are
listed in Table 4. Basically, it worked better on terminal olefins with
lower molecular weight.
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(
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