Magnetic nanoparticle-supported ferrocenylphosphine: A reusable catalyst for hydroformylation of alkene and Mizoroki-Heck olefination

Article abstract of DOI:10.1039/c6ra03859j

We present dopamine (dop) conjugated bis(diphenylphosphino)ferrocenylethylamine (BPPFA) functionalized magnetic nanoparticles (Fe₃O₄). A ferrocene ({η⁵-C₅H₄-PPh₂}Fe{η⁵-C₅H₃-1-PPh₂-2-CH(Me)NH-CH₂-CH₂-4Ph-1,2-OH}) ligand (dop-BPPF) has been prepared by reaction of (1-[1′,2-bis(diphenylphosphino)-ferrocenyl]ethyl acetate) and dopamine hydrochloride to form dop-BPPF, which was characterized by NMR, IR, FTIR, EA and FAB-MS. This ligand was anchored on ultrasmall (6-8 nm) magnetic nanoparticles (MNP) to yield Fe₃O₄@dop-BPPF. The resulting ferrocenylphosphine on magnetic nanoparticles was characterized by SEM, EDS, XRD, TEM, TGA, and VSM. The magnetic nature of the materials was investigated. Fe₃O₄@dop-BPPF exhibits very high catalytic activity for the Pd-catalyzed Mizoroki-Heck reaction and exceptionally high regioselectivity for the Rh-catalyzed hydroformylation reaction with branched aldehydes (up to > 99%). The potential of this Fe₃O₄@dop-BPPF as a reusable catalyst has been studied for the Mizoroki-Heck reaction, and this catalyst was robustly active even after eleven consecutive cycles.

Full text of DOI:10.1039/c6ra03859j

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Magnetic nanoparticle-supported
ferrocenylphosphine: a reusable catalyst for
Cite this: RSC Adv., 2016, 6, 41687
hydroformylation of alkene and Mizoroki–Heck
olefination†
a
M. Nasiruzzaman Shaikh, Md. Abdul Aziz,a Aasif Helal,a Mohamed Bououdina,b
*
Zain H. Yamania and Tae-Jeong Kimc
We present dopamine (dop) conjugated bis(diphenylphosphino)ferrocenylethylamine (BPPFA) functionalized
magnetic nanoparticles (Fe3O4). A ferrocene ({h5-C5H4-PPh2}Fe{h5-C5H3-1-PPh2-2-CH(Me)NH-CH2-CH2-
4Ph-1,2-OH}) ligand (dop-BPPF) has been prepared by reaction of (1-[10,2-bis(diphenylphosphino)-
ferrocenyl]ethyl acetate) and dopamine hydrochloride to form dop-BPPF, which was characterized by
NMR, IR, FTIR, EA and FAB-MS. This ligand was anchored on ultrasmall (6–8 nm) magnetic nanoparticles
(MNP) to yield Fe3O4@dop-BPPF. The resulting ferrocenylphosphine on magnetic nanoparticles was
characterized by SEM, EDS, XRD, TEM, TGA, and VSM. The magnetic nature of the materials was
investigated. Fe3O4@dop-BPPF exhibits very high catalytic activity for the Pd-catalyzed Mizoroki–Heck
reaction and exceptionally high regioselectivity for the Rh-catalyzed hydroformylation reaction with
branched aldehydes (up to > 99%). The potential of this Fe3O4@dop-BPPF as a reusable catalyst has been
studied for the Mizoroki–Heck reaction, and this catalyst was robustly active even after eleven consecutive
cycles.
Received 11th February 2016
Accepted 18th April 2016
DOI: 10.1039/c6ra03859j
www.rsc.org/advances
Ir-based metal complexes have been used for hydroformylation in
the presence of syn gas and are excellent regioselective cata-
lysts.21–23 However, the separation of the catalyst from the reac-
tion mixture by chromatography, distillation and extraction is
highly tedious, cumbersome and economically less viable. In
addition, the valuable metal and ligands used in the process are
not recoverable or reusable, which limits the scope of this process
for cost-effective application.
In this context, the development of environmentally benign,
reusable and efficient organocatalyst is the central goal in
current research to contribute towards a ‘greener’ and safe
environment. Moreover, the use of a readily available feed-
stock, such as highly toxic carbon monoxide, to produce more
expensive functionalized organic intermediates via hydro-
formylation is important. Therefore, extensive efforts have
been focused on the development of alternatives to homoge-
neous catalysis to minimize separation costs and maximize
product purity. Therefore, heterogeneous catalysis has become
an alternative choice.24,25 The heterogenization of catalysts is
based on the immobilization of ligands or metal complexes
over solid supports, such as zeolites,26 polymers,27 silica28 and
cellulose.29 For example, Koten et al. demonstrated the
anchoring of chiral BINAP ligands on the surface of silica,
which is highly stable, robust and easy to functionalize for the
hydrogenation reaction.28 However, the majority of the het-
erogenized catalysts exhibit lower reactivity compared to that of
Introduction
Carbon–carbon bond formation reactions mediated by various
transition metals have emerged as increasingly important
methodologies for the preparation of numerous organic building
blocks, such as drugs1,2 pesticides,3 dye4 and natural products.5,6
Among the many frequently used C–C bond formation protocols,
such as Stille,7 Heck,8 Suzuki,9,10 Kumada,11 and Sonogashira,12
Mizoroki–Heck13 for olenation and alkene hydroformylation14 to
the corresponding aldehyde is important in synthetic organic
and industrial chemistry. These reactions are oen catalyzed by
different phosphine-based homogeneous Pd metal complexes.
For example, PPh3,15 P(o-Tol)3 (ref. 16) and P(Mes)3 (ref. 17) are
used as a monodentate ligands, and dippb (1,4-bis[(diisopropyl)
phosphino]butane),18 dippp (1,4-bis[(diisopropyl)phosphino]
propane)19 and dppf (1,10-bis(diphenylphosphino)ferrocene)20 are
considered bidentate ligands. In a similar fashion, Co-, Rh- and
aCenter of Research Excellence in Nanotechnology (CENT), King Fahd University of
Petroleum and Minerals (KFUPM), Dhahran-31261, Saudi Arabia. E-mail:
mnshaikh@kfupm.edu.sa
bDepartment of Physics, College of Science, University of Bahrain, PO Box 32038,
Kingdom of Bahrain
cInstitute of Biomedical Engineering Research, Medical School, Kyungpook National
University, Buk-gu, Daegu, South Korea 702-911
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra03859j
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their homogeneous counterpart because the catalytic sites dip from BPPFA-OAc (1-[10,2-bis(diphenylphosphino)-ferrocenyl]
inside the solid support and become inaccessible to the ethyl acetate). This organic moiety was anchored on super-
substrate, decreasing the overall reactivity.30,31 Furthermore, paramagnetic iron oxide nanoparticles (SPION) via its phe-
solid catalyst separation processes, such as ltration, emulsi- nolic 1,2-dihydroxide attached to dopamine. The Fe3O4@
cation, and centrifugation, are complex, which affects the dop-BPPF, Fe3O4@dop-BPPF-Rh and Fe3O4@dop-BPPF-Pd
activity and reduces the potential reusability of conventional nanomaterials were characterized using various techniques,
heterogeneous catalysts.32,33
such as TEM, SEM-EDS, XRD, TGA, FTIR, and VSM. Their
Recently, nanoparticles have become an area of interest for catalytic applications to the Pd-catalyzed Mizoroki–Heck and
a wide range of applications in numerous elds. The use of Rh-catalyzed regioselective hydroformylations of olens were
nanoparticles in catalysis is advantageous because (1) nanosize investigated.
particles can be considered equivalent to homogenous systems
due to the reduction in active sites being negligible compared to
that of homogeneous systems. In addition, (2) the highly
exposed surface area of the active component of the catalysts
Experimental
Materials and methods
provides additional proximity between the catalytic centers and All of the chemicals, which were purchased from Sigma-
the reactants, increasing the catalytic activity.30,34 For example, Aldrich, were used as received unless otherwise stated. An
the chemical and physical properties (i.e., shape, size and inert atmosphere and standard Schlenk techniques were used
morphology) of superparamagnetic iron oxide nanoparticles wherever needed. Standard procedures were followed for the
(SPION) can easily be manipulated. The synthesis of SPIONS is dry and deoxygenated solvents. Deionized (DI) water was used
relatively uncomplicated, and the particles are easily function- throughout the experiments. The surface coating was carried
alized.35 Furthermore, SPIONS have the potential to provide out in a low-power bath sonicator (Cole-Parmer model 08892-
catalyst recyclability due to their insolubility in organic solvents 21). The 1H and 13C NMR spectra were recorded on a JEOL
and their distinct magnetic nature, rendering their separation JNM-LA 500 spectrometer with tetramethylsilane (TMS) as the
from the heterogeneous reaction system virtually effortless. internal standard. The 31P NMR spectra was recorded on the
Recently, Wang et al. developed a heterocyclic carbene ligand- same machine using a phosphorous probe and 85% H3PO4 as
coated magnetic system and reported encouraging results for the internal reference. The FTIR spectra were obtained on
the coupling reaction.36 However, the immobilization of the a Nicolet 720 in the range of 400 to 4000 cmꢀ1 using KBr. The
linker, which contains the terminal coordinating group, on thermogravimetric analysis (TGA) data were obtained on
SPION remains a challenge. In a majority of the reported cases, a Mettler-Toleꢀd1o model TGA1 STARe System at a heating rate
amine ligands37 have been used because they stabilize the of 10 ꢁC min in a temperature range of 25–600 ꢁC in an
nanoparticles to prevent aggregation, which produces excellent argon atmosphere. The X-ray diffraction data were collected
results for the hydrogenation,38 coupling39 and oxidation40 on a Rigaku model Ultima-IV diffractometer using Cu-Ka
reactions. In this context, dopamine has become the most radiation.
widely used linker41 because it affords higher stability to the
The nanoparticles were imaged by eld emission scanning
nanoparticle surface and provides a suitable supporting arm for electron microscopy (FESEM) on a LYRA 3 Dual Beam Tescan
further functionalization. To achieve optimum balance between operated at 30 kV. The SEM samples were prepared from etha-
stability and catalytic activity, a suitable donor, such as diphe- nolic suspensions on alumina stabs and coated with gold in an
nylphosphine, could be coordinated to the metal, and this automatic gold coater (Quorum, Q150T E). For the elemental
group could be linked to dopamine to afford excellent catalytic analysis and mapping, the energy dispersive X-ray spectra (EDS)
materials. Therefore, we selected ferrocenyldiphosphine for use were collected on a Lyra 3. The transmission electron microscope
as this donor.
images were collected on a TEM (JEOL, JEM 2011) operated at
During the past few decades, ferrocene-based ligands have 200 kV with a 4k ꢂ 4k CCD camera (Ultra Scan 400SP, Gatan). The
been widely studied due to their electron-rich aromatic struc- TEM samples were prepared by dropwise application of an etha-
tural motifs that undergo electrophilic aromatic substitution. In nolic suspension onto a copper grid followed by drying at room
addition, their relatively low cost, thermal stability, high toler- temperature. The catalytic reactions were performed in a STEM
ance to moisture and oxygen and very unique chemical prop- Omni® 10-place reaction station and a Teon-lined autoclave
erties make these materials attractive. Despite the impressive from HiTech, USA (model: M010SSG0010-E129A-00022-1D1101),
progress in ferrocene-based homogeneous catalysis, the use of which was equipped with a pressure gauge and mechanical
ferrocene in heterogeneous catalysis has remained largely stirrer. The magnetic susceptibilities were measured using
unexplored. Therefore, ferrocenylphosphine with its unique a vibrating sample magnetometer (VSM, model PMC Micromag
stereochemical properties and various prospective coordination 3900) that was equipped with a 1 tesla magnet at room temper-
modes and superparamagnetic iron oxide nanoparticles were ature. The products were identied using GCMS 2010 Plus from
combined for use in regioselective catalytic reactions in a low- Shimadzu, Japan. The syntheses of N,N-dimethylferrocenyl ethyl
cost and environmentally friendly manner.
amine (FA), N,N-dimethyl-1-[-10,2-bis (diphenylphosphino)ferro-
As a part of our continuing efforts,42–44 we report the cenyl] ethyl amine (BPPFA) and 1-[-10,2-bis(diphenylphosphino)
synthesis of a new ferrocene-based ligand (dop-BPPF, {h5-C5H4- ferrocenyl]ethyl acetate (BPPFA-OAc) were performed according to
PPh2}Fe{h5-C5H3-1-PPh2-2-CH(Me)NH-CH2-CH2-4C6H3-1,2-OH}) previously reported procedures.45,46
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General procedure
Synthesis of Fe3O4@{h5-C5H4-PPh2}Fe{h5-C5H3-1-PPh2-2-
CH(Me)NH-CH2-CH2-4Ph-1,2-OH}-M
(Fe3O4@dop-BPPF-M).
Synthesis of {h5-C5H4-PPh2}Fe{h5-C5H3-1-PPh2-2-CH(Me)
NH-CH2-CH2-4Ph-1,2-OH} (dop-BPPF). To a solution of BPPFA-
OAc (0.28 g, 0.43 mmol) in anhydrous methanol (10 mL),
dopamine hydrochloride (0.19 g, 1.0 mmol) and freshly distilled
triethylamine (1 mL) were added under an argon atmosphere.
The mixture was stirred at 85 ꢁC for 12 hours, and then, the
solvent was removed under vacuum. The solid residue was dis-
solved in a minimal amount of methanol and transferred to
a silica gel column for chromatographic separation. The desired
orange band was eluted using a combination of ethyl acetate and
methanol (9 : 1) to produce orange solids aer removal of the
solvents. Recrystallization from methanol/cyclohexane yielded
0.18 g of product (56%). 31P NMR (202 MHz, in DMSO-d6):
d ꢀ28.14 (s, PPh2), ꢀ20.78 (s, PPh2). 1H NMR (DMSO-d6): d 1.30
(d, J ¼ 6.7, 3H, CHCH3), 1.78 (t, 2H, NCH2CH2), 2.29 (t, 2H,
NCH2CH2), 3.55 (m, 3H, C5H3), 4.04–4.49 (m, 4H, C5H4), 6.20 (d,
1H, C6H3), 6.39 (s, 1H, C6H3), 6.60 (d, 1H, C6H3), 7.24–7.50 (m,
20H, PPh2), 8.62 (s, 1H, OH), 8.74 (s, 1H, OH). 13C NMR (DMSO-
d6): 19.03 (CHCH3), 35.12 (NCH2CH2), 69.37 (NCH2CH2), 72.81
(CHCH3), 115.29, 118.91, 128.20, 129.23, 132.11 (C6H3), 132.67,
132.82, 133.04, 134.43, 143.20, 144.81 (C5H3, C5H4 and PPh2).
FTIR in KBr (cmꢀ1): n ¼ 3426 (O–H), 3058 (arC–H), 2920 (Csp3–
H) 1522 (arC–C). FAB-MS (m/z): calc. for C44H41FeNO2P2, 733.198
([M]+); found, 733.196. Anal. calcd for C44H41FeNO2P2$CH3OH:
C, 70.59; H, 5.92; N, 1.83. Found: C, 70.67; H, 6.17; N, 2.01.
Synthesis of Fe3O4@{h5-C5H4-PPh2}Fe{h5-C5H3-1-PPh2-2-
CH(Me)NH-CH2-CH2-4Ph-1,2-OH} (Fe3O4@dop-BPPF). The
magnetic nanoparticles (Fe3O4) were prepared according to
a previously reported procedure.42 The magnetite nanoparticles
(MNPs) were functionalized (Scheme 1) using a previously re-
ported procedure35,42 that we modied as follows: to a suspen-
sion of magnetic nanoparticles (200 mg) in anhydrous
chloroform, the ligand (200 mg) solution in dry methanol was
added under an argon atmosphere. The mixture was sonicated
in a bath sonicator for 6 hours. The surface functionalized
magnetic nanoparticles were collected using a magnet aer
repeated washing with methanol followed by characterization.
FTIR in KBr (cmꢀ1): n ¼ 3435 (O–H + N–H), 2938 (arC–H), 1428
(arC–C), 590 (Fe–O).
The magnetites nanoparticles (100 mg) in chloroform was
sonicated for 1 hour. The solution of [Rh(NBD)Cl]2 (0.015
mmol), slightly excess, in dichloromethane was added to the
suspension and stirred for 4 hours under argon atmosphere.
The materials was collected and washed with dichloromethane
to remove unreacted metal precursor. The same procedure was
followed with the Fe3O4@dop-BPPF-Pd by replacing Rh with
[Pd(C3H5)Cl]2 (0.015 mmol).
Typical procedure for the catalytic hydroformylation reaction
This reaction was carried out in a functional fume hood tted
with good suction. The functionalized magnetic nanoparticles,
Fe3O4@dop-BPPF-Rh (50 mg), styrene (1.0 mmol, 0.12 mL) and
freshly distilled THF (10 mL) were added to a Teon-lined
autoclave equipped with a pressure gauge and a mechanical
stirrer under an argon atmosphere. Next, the inert atmosphere
was replaced with a mild pressure release of CO/H2 gas for three
cycles. Then, the autoclave was pressurized with CO/H2 (1 : 1) at
ꢁ
1000 psi, and the temperature was maintained at 45 C. Aer
completion of the reaction, the pressure was released, and the
sample was passed through a short silica gel column followed
by injection into a GC to determine the conversion and regio-
selectivity values.
Typical procedure for the catalytic Mizoriki–Heck reaction
This reaction was performed in a parallel reactor 10 place
reaction tube tted with a magnetic stirrer and a Teon stopper.
To a suspension of functionalized magnetic nanoparticles,
Fe3O4@dop-BPPF-Pd (50 mg) in DMF : water (1 : 1) (10 mL),
styrene (1.0 mmol, 0.12 mL) and potassium hydroxide (1.0
mmol, 56 mg) were added. The temperature was maintained at
90 ꢁC. The progress of the reaction was monitored by GC, which
was connected to a mass detector, and the product was extrac-
ted using ethyl acetate. The concentrated solution was passed
through a short silica gel column and eluted with hexane : ethyl
acetate (9 : 1).
Results and discussion
Synthesis
Magnetite nanoparticles 6–8 nm in size were prepared by
reaction of divalent and trivalent iron in a 1 : 2 ratio in an
alkaline medium at room temperature under an argon atmo-
sphere with constant stirring (500 rpm). The pH of the solution
was held constant with the periodic addition of conc. NH4OH
for 4 hours. A black precipitate was collected using a magnet
and washed with DI water several times to remove any unreac-
ted iron precursors.
Scheme 1 shows the preparation route for the formation of
dopamine-functionalized ferrocenylphosphine. The synthetic
route involved the preparation of N,N-dimethyl-1-
ferrocenylethylamine (FA) followed by dilithiation and reac-
tion with chlorodiphenylphosphine to afford BPPFA47 (see the
ESI†). The freshly prepared BPPFA was acetylated with the
Scheme 1 Synthesis of Fe3O4@dop-BPPF-Pd and Fe3O4@dop-BPPF-
Rh.
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replacement –NMe2 functional group by reaction with acetic dopamine at 6.20, 6.39 and 6.60 ppm conrmed the formation
anhydride at 100 C for 1 hour to yield BPPFA-OAc.46
of the desired compound, and this compound was further
ꢁ
Dopamine hydrochloride was made soluble in anhydrous characterized by FAB-mass spectrometry and exhibited the
methanol in the presence of excess freshly distilled trimethyl- characteristic molecular ion peak (m/z ¼ 733.196) (see the ESI†).
amine under an argon atmosphere with stirring. The solution
Fig. 1a–d shows the TEM images of Fe3O4 (1a) Fe3O4@dop-
consisting of BPPFA-OAc in methanol was added to the dopa- BPPF, Fe3O4@dop-BPPF-Pd and Fe3O4@dop-BPPF-Rh the
mine solution and reuxed for 12 hours at 85 ꢁC to yield an results indicate that spherically shaped uniformly distributed
orange color solid in good yield. Ferrocenylphosphine was nanosize particles were formed with an average diameter of 6–8
linked with dopamine, which was used as an anchoring unit on nm. The high-resolution TEM and selected area electron
the surface of the magnetic nanoparticles. Bidentate enediol diffraction (SAED) images are shown in Fig. 1e and f respec-
ligands provide higher stability and tight binding to iron oxide tively, and the inter planar distance was determined to be
by transforming under-coordinated Fe surface sites back to
a bulk-like octahedral lattice structure for oxygen-coordinated
magnetites,48 and this behavior is further supported by the
Langmuir isotherm, which indicated that the adsorption of
dopamine via the 1,2-dihydroxyl functional group is more
favorable than its desorption from the metal nanoparticles
surface.49 Therefore, we developed a system with a new organic
ligand-coated magnetic nanostructure for use in catalytic
organic transformation reactions.
Characterization
Structural conrmation of the new dopamine conjugated fer-
rocenylphosphine was based on spectroscopic and analytical
analyses. Characteristic singlets appeared in the highly shielded
(upeld) region (ꢀ20 and ꢀ28 ppm) in the 31P NMR spectra and
were assigned to the diphenylphosphine attached to the ferro-
cene ring (see the ESI†). The presence of ferrocenyl ring protons
in the 3.5–4.5 ppm region, an axial methyl proton chemical shi
Fig. 2 XRD pattern of the (a) Fe3O4 and (b) Fe3O4@dop-BPPF (c)
(d) at 1.30 ppm and three protons of the phenyl ring of Fe3O4@dop-BPPF-Pd (d) Fe3O4@dop-BPPF-Rh.
Fig. 1 TEM images of (a) Fe3O4 and (b) Fe3O4@dop-BPPF (c) Fe3O4@dop-BPPF-Pd (d) Fe3O4@dop-BPPF-Rh (e) HRTEM image of Fe3O4@dop-
BPPF-Pd and (f) SAED of Fe3O4@dop-BPPF-Pd.
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consistent with the literature data.50 The SAED data also
exhibited higher order crystallinity, which was further
conrmed by the X-ray diffraction (XRD) (Fig. 2) signature of the
nanomaterial. The peaks located at 30.22ꢁ, 35.70ꢁ, 43.10ꢁ,
53.40ꢁ, 57.10ꢁ and 63.20ꢁ indicate the formation of a nano-
crystalline cubic (Fd3m) spinel Fe3O4 nanostructure (JCPDS card
no. 01-075-0449).51 Therefore, coating with dop-BPPF followed
by addition with Pd/Rh did not alter the original crystal struc-
ture of the parent compound (Fe3O4). Qualitative and quanti-
tative phase analyses were carried out using the Rietveld
method. The renement results and Rietveld gures (see the
ESI†) also conrmed the formation of a single phase (goodness
t factor was close to 1). The calculated crystallite size was
determined to be approximately 8.5 nm for all of the samples,
which is in good agreement with the size obtained from TEM
analysis. The calculated lattice parameter was approximately
ꢀ
8.36 A, which is close to that of bulk magnetite. Elemental
Fig. 4 Magnetic hysteresis loops of the (a) Fe3O4 (b) Fe3O4@dop-
BPPF (c) Fe3O4@dop-BPPF-Pd (d) Fe3O4@dop-BPPF-Rh at room
temperature with 1 tesla magnet (e) Fe3O4@dop-BPPF-Rh in presence
of a magnet (f) The Mr and Hc in low M and H values. Inset for lower M
and H values showing clearly Mr and Hc.
mapping (Fig. 3) analysis indicated the uniform anchoring of
the ferrocenylphosphine ligands and its subsequent presence
with the metal (i.e., Rh and Pd) on the surface of the nano-
particles, and the existence of these elements were conrmed by
the EDS results. The Fourier transform infrared (FTIR) spec-
troscopic data revealed a vibration red shi of Fe–O by 7 nm
from 583 nm for the parent magnetite with a bare surface. The
characteristic aromatic C–H stretching at 2938 cmꢀ1 and
aromatic C–C at 1428 cmꢀ1 conrmed the presence of the
ligand on the surface. The thermal stabilities of the ligand were
investigated, and the stepwise weight loss prole was deter-
mined under an argon atmosphere in a temperature range of
25–600 ꢁC (see the ESI†). The amount of weight loss was
determined to be approximately 14%, which indicated that the
amount of loading on the nanoparticle surface was 0.2 mmol of
dop-BPPF per gram of magnetic nanoparticles. These data were
further conrmed by the amount of phosphine determined
from the EDS results.
complexation processes. However, the saturation magnetiza-
tion value slightly decreased due to coating and complexation
(dop-BPPF, Pd and Rh). Therefore, these coating and existence
of metal (Pd/Rh) did not substantially affect the bulk magneti-
zation, which is very important for the separation process, and
these data were further conrmed by the physical use of
a magnet near to the vial containing the particles.
Catalysis
Hydroformylation reactions. The catalytic activity was eval-
uated using various substituted styrenes and n-alkenes at 45 ꢁC
with a mixture of carbon monoxide and hydrogen (1 : 1) under
a pressure of 1000 psi. The results are shown in Table 1. The
optimization of the conditions was performed using styrene as
The recorded magnetic data revealed the superparamagnetic
nature of all of the samples (Fig. 4) at room temperature. Prior
to coating, the magnetization of the bare surface of the
magnetites (Fe3O4) was 67 emu gꢀ1, and the magnetization the
surface-coated nanoparticles (Fe3O4@dop-BPPF) was 58 emu
gꢀ1. It is important to note that the coercivity (Hc) and rema-
nence (Mr) are not affected by the surface functionalization and
ꢁ
a model substrate. At 45 C, 85% conversion of styrene to the
corresponding aldehyde was achieved with a branched (B) to
linear (L) ratio of 8 : 1 at 200 psi (entry #1). As the reaction
temperature increased to 70 ꢁC, the yield improved but the
Fig. 3 Elemental mapping of (a) iron, (b) phosphorous (c) palladium and (d) rhodium of Fe3O4@dop-BPPF.
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Table 1 Hydroformylationa of olefins using Fe3O4@dop-BPPF-Rh as catalysts
Time
(h)
Temp
(ꢁC)
Conv.c
(%)
Branch (B)
(%)
Linear (L)
(%)
Ratio
(B : L)
Entry
Substrate
Solv.
1b
2b
3
4
5
6
7
8
9
10
11
12
13
Styrene
Styrene
Styrene
Styrene
9
10
8
THF
THF
THF
45
70
45
45
45
45
45
45
45
45
45
45
45
85
91
>99
>99
86
>99
>99
>99
>99
>99
>99
96
88.6
48.1
94.5
96.4
85.4
93.4
98.1
97.2
98.6
99
11.4
51.9
5.5
3.6
14.6
6.6
1.9
2.8
1.4
1
8 : 1
0.9 : 1
17 : 1
28 : 1
6 : 1
14 : 1
52 : 1
35 : 1
70 : 1
99 : 1
99 : 1
nd
8
DCM
No solv.
THF
DCM
DCM
DCM
DCM
DCM
DCM
DCM
Styrene
14
14
14
14
12
13
13
16
16
4-Methylstyrene
4-Methylstyrene
4-Vinylanisole
4-Chlorosyrene
3-Nitrostyrene
2-Bromostyrene
Vinylbenzoate
1-Octene
99
nd
—
1
nd
100
85
0 : 100
a
1 mmol of styrene in 10 mL anhydrous solvent under syn gas (CO : H2 1 : 1) pressure using 50 mg of Fe3O4@dop-BPPF-Rh and Rh-metal precursor.
Done at 200 psi. Determined by GC and identied by GC-MS; nd: not determined.
b
c
regioselectivity was lost (entry #2). The solvent polarity plays an
The recyclability of the catalysts was investigated by
important role in the selectivity. Based on the results in Table 1, employing the optimized reaction conditions. Aer the rst
a more polar solvent negatively affected the selectivity. Among round of catalysis, the nanocatalysts were sufficiently washed
all of the tested solvents, dichloromethane was the most effi- with dichloromethane to remove any unwanted materials and
cient solvent for this reaction. For example, a higher selectivity reused for the 2nd round of catalysis without the addition of
(B : L ¼ 17 : 1) was obtained by employing a pressure of 1000 psi more Rh metal precursor. A gradual loss in the catalytic activity
in THF at 45 ꢁC. However, a substantial improvement was was observed aer the 4th run, which may be due to a higher
observed when the same reaction was performed in dichloro- pressure being employed in the reaction system, and the active
methane, and the regioselectivity increased to 28 : 1 from 17 : 1 catalyst was leached from the surface of the magnetic
(entries #3 and 4) and 52 : 1 from 14 : 1 (entries #6 and 7) for nanoparticles.
styrene and 4-methylstyrene, respectively. This excellent selec-
tivity towards the branched aldehyde can be hypothesized that
may be due to (1) the metal binding sites being far away from
the metal nanoparticle surface, causing little interference with
the Rh metal center. In addition, (2) the steric environment
around the phosphine coordinated to the metal resulted in the
predominant production of one isomer. We employed different
types of electron-withdrawing and donating groups on the
styrene substrate for the hydroformylation reaction. Although
no noticeable change in the reactivity was observed, a profound
effect was observed for the selectivity. The selectivity ratio for
the branched to linear isomers of nitrostyrene and bromostyr-
ene was 99 : 1 (entries #10 and 11).
We also investigated the hydroformylation of styrene under
solvent-free conditions and achieved 86% conversion (entry #5)
with 85% branched isomer. For n-alkene, the reactivity of the
catalyst is slow, and the conversion of 1-octene (entry #14)
reached to 85% but the opposite selectivity exhibited
a maximum value (B : L ¼ 0 : 100). This result is consistent with
previously reported data.25
Table 2 Optimization of Mizoroki–Heck reaction between iodo-
benzene and styrenea
Entry
Base
Temp (oC)
Solvent
Conversionb (%)
1
2
3
4
5
6
7
KOH
KOH
K2CO3
Et3N
KOH
KOH
KOH
60
95
95
95
95
95
95
DMF–H2O (1 : 1)
DMF–H2O (1 : 1)
DMF–H2O (1 : 1)
DMF–H2O (1 : 1)
H2O
50
99
69
56
67
44
81
Toluene
DMF
a
Conversion measured aer 30 minutes of reaction and the
b
conversions are based on iodobenzene. Determined by GC and
identied by GC-MS.
41692 | RSC Adv., 2016, 6, 41687–41695
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Mizoroki–Heck reactions. To optimize the reaction condi-
RSC Advances
tions of the Mizoriki–Heck reaction, styrene and iodobenzene
were chosen as the model substrates to evaluate the catalytic
activity. The results are shown in Table 2. The effect of the
temperature was investigated. A higher temperature was
determined to be effective, which was conrmed by the results
in entries #1 and 2. At 95 ꢁC, styrene was quantitatively con-
verted to its corresponding product. However, at a lower
temperature, the conversion was 50% (entry #1). In this reac-
tion, the base plays a crucial role in the regeneration of Pd active
species. Therefore, the K2CO3, Et3N and KOH bases were used
in the DMF : H2O (1 : 1) mixture as a solvent, and the highest
conversion was obtained using KOH (entry #2) compared to that
using potassium carbonate or triethylamine (entries #3 and 4).
The solvent effect was thoroughly investigated by employing
a series of solvent systems, such as water, toluene, DMF and
DMF : water (1 : 1). The catalytic yield in pure water was only 67
(entry #5), which may be due to the organic substrate, which is
highly insoluble in pure water, not being in sufficient contact
with the metal reaction sites. However, the DMF : water (1 : 1)
mixture was a better solvent compared to that of pure DMF
(entries #2 and 7).
Fig. 5 (a) Re-usability studies of Mizoriki–Heck reaction of styrene and
iodobenzene at 95 ꢁC, in mixture of solvent DMF : H2O (1 : 1) using
KOH as base (b) TEM image of the recovered catalyst.
Using the optimal reaction conditions, the coupling reaction
was extended to a range of substituted styrene substrates to
explore the scope of the newly developed catalytic system, and
the results are summarized in Table 3. For example, as ex-
pected, bromobenzene was much less reactive with styrene than
the corresponding iodobenzene (entries #1 and 2). However,
prolonging the reaction time to 2–24 hours resulted in quanti-
tative conversion. This result indicated the higher stability of
the catalyst even aer increasing the reaction time. The
electron-withdrawing group in the para and meta of styrene
(entries #7–10) decreased the reaction rate. For example, using
4-chlorostyrene (entry #7 and 8), the maximum conversion
was 69% aer 24 hour, and the same trend was observed for
3-nitrostyrene (entry #10), which yielded 85% of the coupling
product.
Table 3 Mizoroki–Heck reactiona between arylhalide and substituted
styrene
The reusability of the nanocatalysts was investigating using
the reaction of styrene and iodobenzene at 95 ꢁC, and the
results are shown in Fig. 5 as a bar diagram. Aer completion of
the coupling reaction, the catalyst was collected by placing an
external magnet at the bottom of the reaction vessel, and the
solution was decanted for work up and GC measurements. The
collected nanomaterials were repeatedly washed with ethyl
acetate and water prior to use in the next round of catalysis. The
catalyst exhibited a consistent activity up to the 10th consecutive
cycle aer the reaction time was increased to 12 hours. The TEM
image (Fig. 5b) was obtained for the catalyst recovered aer 10th
cycle and no signicant change was observed. Intrigued by its
robustness, the collected catalysts from the 10th cycles were
placed in the same coupling reaction for 30 days, and surpris-
ingly, the observed loss of activity remained almost the same.
Entry
Substrate (R)
Halide (X)
Time (min)
Conversionb
1
2
H
H
I
Br
30
30
60
120
24 h
30
30
60
120
30
30
60
120
30
30
60
120
24 h
30
60
30
99
78
80
96
99
96
87
95
98
99
77
94
96
98
35
60
66
69
94
97
22
27
85
96
3
4
4-CH3
4-CH3
I
Br
5
6
4-OCH3
4-OCH3
I
Br
7
8
4-Cl
4-Cl
I
Br
Conclusion
In summary, we have successfully developed ferrocenylphos-
phine ligand-coated magnetic nanomaterials for the hydro-
formylation and Mizoroki–Heck reactions. The use of the
nanocatalyst in regioselective reactions of vinyl arenes and n-
alkene resulted in very high branched isomer yields with
excellent reactivity. The reaction was straightforward. In addi-
tion, no hydrogenated product was observed in the Rh-catalyzed
hydroformylation, and no biphenyl product was observed in the
Pd-catalyzed Mizoroki–Heck reaction. This system can be
employed as a green catalyst in the hydroformylation reaction
9
3-NO2
3-NO2
I
10
Br
60
24 h
30
11
2-Br
I
a
Reactions were carried out at 95 ꢁC in DMF : H2O (1 : 1) using KOH as
base and Fe3O4@dop-BPPF-Pd; conversions are based on halobenzene.
b
Determined by GC and identied by GC-MS.
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without the use of any organic solvents. This material is highly 22 C. Kubis, M. Sawall, A. Block, K. Neymeyr, R. Ludwig,
robust, thermally stable and reusable for many consecutive A. Bçrner and D. Selent, Chem.–Eur. J., 2014, 20, 11921.
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ability may only be limited under high pressures (1000 psi or R. Franke and M. Beller, Angew. Chem., Int. Ed., 2011, 50, 280.
more) in the rhodium-catalyzed reaction. We believe that our 24 P. Wang, X. Liu, J. Yang, Y. Yang, L. Zhang, Q. Yang and C. Li,
simple synthetic strategy will open up a new area related to the J. Mater. Chem., 2009, 19, 8009.
attachment of functionalized ferrocene to metal oxide nano- 25 R. Abu-Reziq, H. Alper, D. Wang and M. L. Post, J. Am. Chem.
particle surfaces for various regio- and heterogeneous catalytic Soc., 2006, 128, 5279.
applications. The mechanism of action of the unusually high 26 (a) H. Zhang, Y. Zou, Y.-M. Wang, Y. Shen and X. Zheng,
selectivity and its asymmetric version (i.e., enantioselective
hydrogenation, allylic alkylation, Michael addition and cyclo-
propanation) are currently under process in our lab.
Chem.–Eur. J., 2014, 20, 7830; (b) Z.-M. Li, Y. Zhou,
D.-J. Tao, W. Huang, X.-S. Chen and Z. Yang, RSC Adv.,
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27 (a) H. Zhang, W. Yang and J. Deng, Polymer, 2015, 80, 115; (b)
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Acknowledgements
MNS gratefully acknowledges the National Plan for Science, 28 (a) Y. Maegawa and S. Inagaki, Dalton Trans., 2015, 44,
Technology and Innovation (MAARIFAH)-King Abdulaziz City
for Science and Technology through the Science and Tech-
nology Unit at King Fahd University of Petroleum and Minerals
(KFUPM), the Kingdom of Saudi Arabia, award number 15-
NAN4650-04.
13007; (b) J. M. Bolivar, S. Schelch, T. Mayr and
B. Nidetzky, ACS Catal., 2015, 5, 5984; (c) M. Rimoldi,
D. Fodor, J. A. van Bokhoven and A. Mezzetti, Catal. Sci.
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Technol., 2015, 5, 4575; (d) A. R. McDonald, C. Muller,
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29 S. Zhou, M. Johnson and J. G. C. Veinot, Chem. Commun.,
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