Immobilized chiral rhodium nanoparticles stabilized by chiral P-ligands as efficient catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

Article abstract of DOI:10.1016/j.mcat.2019.110551

This work reports the efficient synthesis of enantio-enriched alcohols by asymmetric hydrogenation of 1-phenyl-1,2-propanedione using chiral nanoparticles (NPs) supported on SiO₂. The chiral catalysts were synthesized by reducing the [Rh(μ?OCH₃)(C₈H₁₂)]₂ precursor under H₂ in the presence of P-chiral ligands as stabilizers and SiO₂ as support. Synthesis of catalysts in mild conditions was performed from labile organometallic precursor and chiral ligands provided small and well defined chiral nanoparticles (≤ 3 nm). The catalysts were characterized by XPS, HR-TEM, EDS, XRD and N₂ physisorption isotherm. The physical chemical properties of the materials were correlated with the catalytic results obtained in the asymmetric hydrogenation of 1-phenyl-1,2-propanedione. In 1-phenyl-1,2-propanedione hydrogenation the best results using chiral catalysts allowed 98% conversion and enantiomeric excess of 67% to (R)-1-hydroxy-1-phenyl-propan-2-one and 59% for (R)-2-hydroxy-1-phenylpropan-1-one. Catalyst recycling studies revealed that chiral nanoparticles immobilized on SiO₂ are stable. These catalysts do not need extra amount of chiral modifier or inducer added in situ and could be reused without loss of enantioselectivity.

Full text of DOI:10.1016/j.mcat.2019.110551

MolecularCatalysis477(2019)110551
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Immobilized chiral rhodium nanoparticles stabilized by chiral P-ligands as
efficient catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-
propanedione
Doris Ruiza,⁎, Päivi Mäki-Arvelab, Atte Ahob, Ricardo Chimentãoa, Carmen Claverc, Cyril Godardc,
José L.G. Fierrod, Dmitry Yu. Murzinb
a Physical Chemistry Department, Faculty of Chemistry, University of Concepcion, 407037, Concepcion, Chile
b Johan Gadolin Process Chemistry Centre, Åbo Akademi University, FI-20500 Turku/Åbo, Finland
c
́
́
́
Departament de Quımica Fısica i Inorgànica, Facultat de Quımica, Universitat Rovira I Virgili, 43005 Tarragona, Spain
d Institute of Catalysis and Petrochemistry (CSIC), Cantoblanco, 28049, Madrid, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords:
Chiral nanoparticles
Rhodium
Enantioselective hydrogenation
Recyclable catalysts
This work reports the efficient synthesis of enantio-enriched alcohols by asymmetric hydrogenation of 1-phenyl-
1,2-propanedione using chiral nanoparticles (NPs) supported on SiO2. The chiral catalysts were synthesized by
reducing the [Rh(μ−OCH3)(C8H12)]2 precursor under H2 in the presence of P-chiral ligands as stabilizers and
SiO2 as support. Synthesis of catalysts in mild conditions was performed from labile organometallic precursor
and chiral ligands provided small and well defined chiral nanoparticles (≤ 3 nm). The catalysts were char-
acterized by XPS, HR-TEM, EDS, XRD and N2 physisorption isotherm. The physical chemical properties of the
materials were correlated with the catalytic results obtained in the asymmetric hydrogenation of 1-phenyl-1,2-
propanedione. In 1-phenyl-1,2-propanedione hydrogenation the best results using chiral catalysts allowed 98%
conversion and enantiomeric excess of 67% to (R)-1-hydroxy-1-phenyl-propan-2-one and 59% for (R)-2-hy-
droxy-1-phenylpropan-1-one. Catalyst recycling studies revealed that chiral nanoparticles immobilized on SiO2
are stable. These catalysts do not need extra amount of chiral modifier or inducer added in situ and could be
reused without loss of enantioselectivity.
1. Introduction
stringent environmental requirements require clean technologies re-
lated to “green chemistry” principles such as milder operation condi-
Asymmetric synthesis by homogeneous and heterogeneous catalysis
is commonly used for the production of optically pure chemicals for
pharmaceuticals, flavoring and fragrances [1,2]. Specifically a con-
siderable attention has been focused on the hydrogenation of α,β-un-
saturated carbonyl compounds and α-ketoesters of high importance in
the production of building blocks for fine chemicals industry [2,3]. One
of the most studied α-ketoester, ethyl pyruvate, has been originally
reported by Orito et al. [4,5] over cinchona alkaloid-modified platinum
catalysts. Since then, a number of heterogeneous systems have been
used in enantioselective hydrogenation [6–9]. High activity was re-
ported in most cases, however a chiral inducer or modifier could be not
recovered with the catalyst as it is added in situ and remains in the
reaction media [10,11]. Otherwise, high activity and excellent se-
lectivity obtained by a variety of homogeneous catalysts have been
reported in asymmetric hydrogenations [12,13]. However, recent more
tions, high efficiency, reduction of emissions and mainly application of
recyclable catalysts. It is, however, well known that homogeneous
catalysts are difficult to recover from the reaction media [12].
Taking advantage of the high efficiency of catalysts [14] and ligands
[15] used in homogeneous processes and feasibility of reusing hetero-
geneous catalysts, an increase in the synthetic scope of immobilization
of these species has been widely studied in the last years [16]. In this
field, chiral modification of metal surfaces has expanded successfully
along the years [17–19]. A variety of experimental techniques provides
chiral materials [20,21] including supported asymmetric homogeneous
catalysts [20], chiral modifiers with heterogeneous supported metal
catalysts [22–30], colloidal metal particles stabilized with chiral li-
gands [18,19,31–33], grafted chiral modifiers on supports [34–36],
functionalized polymers [37] and chiral nanoparticles immobilized on
metal oxide surfaces [20]. Typically SiO2, Al2O3 or TiO2 are the most
⁎ Corresponding author.
E-mail address: doruiz@udec.cl (D. Ruiz).
https://doi.org/10.1016/j.mcat.2019.110551
Received 11 April 2019; Received in revised form 27 June 2019; Accepted 2 August 2019
Availableonline24August2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
used supports for this kind of heterogenization [20,36,38]. Contrary to
polymeric matrices often used for anchoring ligands or organometallic
complexes, mesoporous supports have the advantage of strong ad-
sorption and good mechanical strength [20].
In the field of transition metal NPs, several methods of stabilization
have been reported [39–46]. In the context of catalysis, control of size,
shape and dispersion of metals on support surface is desirable due to
their influence on the activity, selectivity and recycling [35,37]. This
stabilization can be provided by traditional organic ligands [47–56] or
polymers [38,57,58], and ionic liquids [59]. One of the simplest ways
to incorporate organic compounds onto the surface is by adsorption
which is possible through functional groups as phenyl rings or het-
eroatoms such as P or N [50,55,60,61].
(diphenylphosphino)butane) and TANIAPHOS, ≥99%; ((RP)-1-[(R)-α-
(dimethylamino)-2-(diphenylphosphino)benzyl]-2-diphenylphosphino
ferrocene).
The following chemicals, nn-pentane (99%), tetrahydrofuran (THF,
99.9%), allylmagnesium chloride (2 mol L−1 in THF), and di-
chloromethane (99.8%), all from Aldrich, and cyclohexane (99.5%),
methanol (99.9%), diethylether (98%) and ethanol (96%), from Merck,
were distilled prior reactions. Precursor and catalyst was prepared
under purified N2 atmosphere. N2 and H2 (99.995%) were purchased
from Linde. SiO2 was heated at 150 °C for 2 h before use to remove
humidity.
2.2. Precursor synthesis
The effect of ligand nature was elucidated in the enantioselective
hydrogenation
of
1-phenyl-1,2-propanedione
(PPD)
Rh(μ-Cl)(C8H12)]2 was synthesized from RhCl3·3H2O (2.0 mmol)
and 1.1 mL of cis, cis-1 5-cyclooctadiene in 20 mL of ethanol [18]. This
solution was stirred under reflux at 70 °C for 3 h giving a yellow pre-
cipitate, which was filtered and washed with diethyl ether collecting
71% of yield. [Rh(μ-Cl)(C8H12)]2 was obtained according to the fol-
lowing reaction:
[19,22–31,33,34,63], which lead to an important intermediate in the
synthesis of drugs [3]. Typically Pt was used as an active metal in en-
antioselective hydrogenation of PPD [19,22–35]. However, recently
also other metals have been investigated in this reaction, such as Rh
[19,63] and Ir [19,62]. Inspired by our previous results in en-
antioselective hydrogenation of PPD giving maximally 72% en-
antiomeric excess of (R)-1-hydroxy-1-phenylpropan-2-one at 57%
conversion level at 25 °C under 40 bar hydrogen in cyclohexane as a
solvent over Rh nanoparticles stabilized by chiral ligands and supported
on SiO2 [19], it was decided to test also other chiral ligands stabilizing
Rh NPs. In the current work the synthesis of catalysts [18] allowed to
obtain clean chiral-surfaces by reduction of an unsaturated metal pre-
cursor under mild conditions on SiO2. The surface modification was
performed by chiral ligands known as efficiently in asymmetric
homogeneous catalysts. Chiral nanoparticles immobilized on SiO2 were
characterized by XPS, HR-TEM, EDS, XRD and N2 physisorption and
tested in hydrogenation of PPD.
2RhCl3 + 2 C8H12 + 2CH3CH2OH → [Rh(μ-Cl)(C8H12)]2 + 4HCl +
2CH3CHO
(1)
[Rh(μ−OCH3)(C8H12)]2 was prepared from [Rh(μ-Cl)(C8H12)]2
(0.36 mmol) in dichloromethane (15 mL). This solution was added to
KOH (0.71 mmol) in methanol (5 mL). Immediately a dark yellow solid,
[Rh(μ−OCH3)(C8H12)]2, was obtained according to the following re-
action:
[Rh(μ-Cl)(C8H12)]2 + 2KOH + 2CH3OH → [Rh(μ−OCH3)(C8H12)]2 +
2KCl + 2H2O
(2)
This solid was mixed with 10 mL of methanol and 15 mL of water.
Then, the solution was filtered, washed and finally dried under vacuum
without further purification allowing 75% of yield.
2. Experimental
All experiments were carried out using standard Schlenk techniques
and vacuum-lines. Substrates and solvents used in this study were
analytical grade and treated by standard methods.
2.3. Catalysts synthesis
The catalysts synthesis was carried out following the procedure of
two steps: Rh chiral nanoparticles synthesis and subsequent support
immobilization. Unsupported and supported NPs catalysts were ob-
tained from [Rh(μ−OCH3)(C8H12)]2 and stabilizers DIPAMP, (-)-DIOP,
(+)-DIOP, TANIAPHOS, MANDYPHOS and BINAP as ligands to provide
chiral surfaces.
Hydrogenation of a prochiral compound, PPD hydrogenation in
Scheme 1, over catalysts synthesized from [Rh(μ−OCH3)(C8H12)]2
precursor and the chiral ligand (-)-DIOP was used to study the ligand
effect on the catalysts synthesis.
2.1. Materials
RhCl3·3H2O (38%), 1-phenyl-1,2-propanedione (99%), cis,cis-1,5-
cyclooctadiene (≥ 95%), KOH (≥85%) and chiral ligands*were used as
received from Aldrich without further purification.
Nomenclature used for chiral ligands*: DIPAMP, ≥95%; ((S,S)-1,2-
bis[(2-methoxyphenyl)(phenylphosphino)]ethane), MANDYPHOS,
≥
97%; ((1R,1′R′)-1,1′-bis(dicyclohexylphosphino)-2,2′-bis[(R)-(di-
methylamino)phenylmethyl]ferrocene), BINAP; ((R)-(+)-2,2′-bis(di-
phenylphosphino)-1,1′-binaphthalene), (+)-DIOP, 98%; ((+)-2,3-O-
Isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane),
Rh precursor and chiral ligands (DIPAMP, (-)-DIOP, (+)-DIOP,
TANIAPHOS, MANDYPHOS and BINAP) with a Rh/Ligand mole ratio of
0.2 were dissolved in 80 mL of THF. For each rhodium precursor, the
reductive treatment was carried out at 25 °C and 3 bar H2 under
(-)-DIOP,
98%;
((-)-2,3-O-Isopropylidene-2,3-dihydroxy-1,4-bis
Scheme 1. Enantioselective hydrogenation of PPD.
2

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
revealed that there were no gas-liquid mass transfer limitations. The
catalyst particles were below 150 μm to suppress the internal mass
transfer limitations.
Table 1
HR-TEM and textural characterization of Rh catalysts from [Rh(μ−OCH3)
(C8H12)]2 precursor stabilized with chiral ligands.
dTEM (nm) DTEM SBET (m2/ dpore
Vpore (cc/
g)
The same conditions were used for the recycling tests, where Rh
(-)-DIOP/SiO2 catalyst was recycled by filtering and washing two times
with n-pentane (15 mL) to remove compounds from the previous ex-
periment. After treatment for 8 h in vacuum at 50 °C, the dried catalysts
were used in the above mentioned conditions. Hydrogenation reaction
over Rhfree NPs was performed using the same amount of Rh used with
supported NPs catalysts.
The samples withdrawn from the reactor at different time intervals
were analyzed using a SHIMADZU QP5050 GC–MS equipped with a
chiral column β-DEX 225 (length 30 m, diameter 0.25 mm). The chro-
matographic program was generated by heating at 1 °C min−1 from 170
to 180 °C, with the column pressure of 90 kPa, column flow of 0.9 mL
min−1, total flow of 30.7 mL min−1 and the split ratio equal to of 20.
Under these conditions, PPD and its hydrogenation products were
identified by comparing their retention times with those of standards.
Moreover, the structure of all compounds was verified by their mass
spectra using GC–MS and the corresponding database. The retention
times for substrate 1-phenyl-1,2-propanedione was 3.787 min, while for
the reaction products they were 4.68; 4.93; 4.26 and 4.37 min, for (R)-
Catalyst
g)
(nm)
Rh(-)-DIOP Nanoparticles 2.4
Rh(-)-DIOP/SiO2
1.1
–
–
–
–
2.4
1.8
2.4
2.5
2.0
2.5
1.1 0.38
0.9 0.51
1.1 0.38
1.3 0.37
0.8 0.46
1.1 0.37
512
563
544
496
543
583
6.2
5.5
6.1
5.7
5.9
5.4
0.81
0.83
0.95
0.75
0.85
0.85
Rh-DIPAMP/SiO2
Rh-MANDYPHOS/SiO2
Rh-BINAP/SiO2
Rh-TANIAPHOS/SiO2
Rh(+)-DIOP/SiO2
dTEM (metal diameter) and DTEM (metal dispersion) determined by TEM.
SBET (surface area), dpore (pore diameter) and Vpore (pore volume) from
Brunauer, Emmett and Teller (BET) and Barrett, Joyner and Halenda (BJH)
models.
magnetic stirring for 40 h, 20 h and 70 h, respectively. Synthesis con-
ditions of stabilized nanoparticles were previously optimized [18].
After synthesis, an appropriate amount of chiral nanoparticles was
added onto dried SiO2 obtaining 1 wt.% of Rh on SiO2. 80 mL of THF
was added to the mixture followed by stirring overnight at 25 °C. Fi-
nally, the chirally modified catalyst was washed with pentane (25 mL)
and dried under vacuum for 3 h at 40 °C. Nomenclature used for cata-
lysts is shown in Table 1.
1-hydroxy-1-phenylpropan-2-one,
(S)-1-hydroxy-1-phenylpropan-2-
one, (S)-2-hydroxy-1-phenylpropan-1-one and (R)-2-hydroxy-1-phe-
nylpropan-1-one, respectively.
The same procedure as mentioned above was also used for pre-
paration of unsupported chiral nanoparticles (Rhfree NPs).
The ligand free 1 wt.% Rh/SiO2 catalyst has been prepared from [Rh
(μ−OCH3)(C8H12)]2 by the same procedure without, however, chiral
ligands to assess if addition of ligands is beneficial for catalytic per-
formance as such addition can be instrumental in regulating the growth
of metallic clusters.
Activity was analyzed in terms of conversion, defined as (c0,A-cA)/
0,A*100%, where c0,A and cA denote the initial reactant concentration
c
and the concentration of A at time t, respectively. The sum of the
concentrations of reactant and products visible in GC analysis has been
calculated as a function of time and denoted as GCLPA.
The initial TOF was calculated after 10 min of reaction time by di-
viding the converted moles of reactant by moles of the metal.
Enantiomeric excess was determined for PPD hydrogenation as
2.4. Catalysts characterization
ee = ([R]-[S])/([R]+[S])x100%
(3)
Metal particle sizes were determined by transmission electron mi-
croscopy using a JEOL JEM-1011 equipment. Over 850 and 300 par-
ticles for NPs and supported catalysts, respectively, were analyzed. X-
Ray Energy Dispersive Spectroscopy and Electron Diffraction were
analyzed using this same equipment.
Nitrogen sorption isotherms at −196 °C were obtained with a
Micromeritics ASAP 2010 (CHEMI) instrument. The samples (100 mg)
were evacuated for 3 h at 150 °C before the surface area measurements.
Brunauer, Emmett and Teller (BET) and Barrett, Joyner and Halenda
(BJH) models were used to calculate the specific surface area, pore
diameter and pore volume in all catalysts tested. The surface areas were
calculated in the range of P/P° = 0.05-0.3.
In PPD hydrogenation (Scheme 1), ee1 and ee2 are referred to (R)-
over the (S)-enantiomer of 1-hydroxy-1-phenylpropan-2-one and 2-hy-
droxy-1-phenylpropan-1-one, respectively.
Regioselectivity (rs) is defined as the ratio between the concentra-
tions of ([R1] + [S1]) enantiomers obtained from hydrogenation of
carbonyl-1 group and ([R2] + [S2]) enantiomers formed from carbonyl-
2 hydrogenation as
rs = [R1]+ [S1]) /([R2]+ [S2])
(4)
3. Results and discussion
XRD analyses was performed using a Rigatu New X-Ray “Geigerflex”
D/max-IIC (40 Kv, 2 mA) diffractometer in the 2θ range of 10° to 90°
(λ = 1.54056 Aº) at 1°/min.
3.1. Catalysts characterization
Photoelectron spectra (XPS) were recorded using a Fisons Escalab
200R spectrometer equipped with a hemispherical analyzer using Mg
Kα X-ray radiation (hν =1253.6 eV) at 10 mA and 12 kV.
The textural parameters of supported and unsupported NPS from
[Rh(μ−OCH3)(C8H12)]2 precursor [18,64,65] are shown in Table 1.
HR-TEM results revealed that all catalysts from NPs with ligands ex-
hibited smaller metal particle sizes (< 3 nm), compared to ligand free
NPs and 1 wt.% Rh/SiO2 catalyst (both ca. 5.1 nm).
The chemical structure of the synthesized precursor was confirmed
by NMR 1H in a Varian-Mercury 400 MHz equipment.
H2 as a reducing agent under mild conditions generates highly re-
producible particle sizes from [Rh(μ−OCH3)(C8H12)]2 releasing
CH3OH and inert C8H16 species from their hydrogenation. Specifically,
a small metal size is directly related to the presence of chiral ligands in
the synthesis of nanoparticles during the metal precursor reduction.
Fig. 1 displays a comparison of unsupported and supported, nano-
particles stabilized with (-)-DIOP.
Table 1 shows HR-TEM results for supported particles from [Rh
(μ−OCH3)(C8H12)]2 and different chiral ligands confirming minor
changes in metal dispersion up to 51% and diameters ≤ 2.5 nm. BINAP,
DIPAMP, TANIAPHOS, MANDYPHOS, (+)-DIOP and (-)-DIOP ligands
2.5. Hydrogenation reactions
Reactions were performed at 40 bar of H2 pressure, 25 °C and stir-
ring speed of 800 rpm to avoid external mass transfer limitations.
Supported and unsupported NPs were tested as catalysts in hydro-
genation reactions with a [substrate/metal] molar ratio of 100 in 50 mL
of cyclohexane as a solvent. A stainless steel semibatch reactor coated
with teflon was used for PPD enantioselective hydrogenation. In the
preliminary experiments, different amounts of catalyst were used to
investigate a potential impact of gas-liquid mass transfer and the results
3

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Fig. 1. Electron micrographs and size distribution of a) unsupported Rh Chiral NPs and b) 1 wt.% Rh/SiO2 chiral catalyst from [Rh(μ−OCH3)(C8H12)]2 precursor.
(Fig. 2) allow to control the metal agglomeration and provide chiral
surfaces. For this kind of systems it has been reported that stabilization
occurs by adsorption of phenyl rings or heteroatoms as P or N (such as
those present in Fig. 2) on the metal surface [50].
necessary using these catalysts. The reason for such behavior is that
ligands or organic compounds acting as stabilizers for metal surface
generally prevent metal oxidation [20,50].
Binding energies of O1s and Si2p core-levels appeared at 532.6 and
103.4 eV, respectively. All catalysts showed binding energies centered
at 307.0 and 309.0 eV for Rh3d5/2 core level corresponding to both Rhº
and Rhδ+, respectively (Fig. 3). Only for unsupported NPs and Rh-DI-
PAMP/SiO2 catalysts it was possible to determine phosphorus BE P2p
on the surface at 133.1 eV, confirming the presence of ligands on the
surface. In other supported nanoparticles it was not possible to detect
heteroatoms due to a high amount of SiO2 (99 wt.%) and Rh im-
mobilization occurring preferably inside the bulk support, which is in
agreement with nitrogen physisorption (Table 1). Rh-DIPAMP on sur-
face could be explained by the presence of methoxy substituents in the
structure of the chiral ligand interacting with the Si−OH groups on the
surface.
The characterization results reported in this work showed that
synthesis of catalysts from [Rh(μ−OCH3)(C8H12)]2 in the presence of
chiral ligand (-)-DIOP is very reproducible. Regarding the use of chiral
ligands, (-)-DIOP, DIPAMP and BINAP showed the highest Rh/Si ratio
on the surface (Table 2). Differences in the ratio of metal on surface
found are associated with the stabilizer ligand nature and therefore its
interaction with the surface during the synthesis of metal clusters.
BET specific surface areas vary between 496 and 583 m2 g−1 and
the isotherms correspond to type IV (IUPAC classification). The specific
surface are of the neat SiO2 support was 550 m2 g−1. This value in
comparison with the value of supported metals illustrate that in-
troduction of the metals did not result in significant alterations of the
surface area.
A low metal content and small metal particle sizes were also verified
by XRD which did not show any signals for Rh. A broad peak between
15 and 35° with a maximum at 2θ = 22.0° corresponding to SiO2 was
present in all catalysts.
Electron diffraction allowed verifying reduced rhodium species and
interplanar spacing of dhkl=2.1658 Å. By X-Ray Energy Dispersive
Spectroscopy was possible to identify Rh and SiO2.
The degree of reduction and the surface composition were estab-
lished by XPS. Table 2 summarizes atomic percentages and atomic
surface ratios of Rh catalysts. The catalyst from chiral stabilized NPs
showed a high content of Rh on the surface. A high percentage of re-
duced Rh was obtained without any reduction pretreatment. XPS ana-
lysis confirmed that a small flow or stream in H2 allows reduction of
rhodium species on the catalyst surface, therefore a conventional re-
duction procedure at a high temperature prior to each reaction is not
Fig. 2. Chiral ligands: a) DIPAMP, b) MANDYPHOS, c) (+)-DIOP, d) (-)-DIOP, e) BINAP and f) TANIAPHOS.
4

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Table 2
Binding energies of core levels and atomic surface ratio of Rh catalysts.
Catalyst
Rh 3d5/2 (eV)
P 2p (eV)
P at,
%
Rh at, %
Rh/P at
ratio
Rh/Si at ratio
Rh(-)-DIOP Nanoparticles
Rh(-)-DIOP/SiO2
Rh-TANIAPHOS/SiO2
307.1 (76); 309.2 (24)
307.1 (80); 309.0 (20)
307.0 (84);
133.0
–
–
8.3
–
–
7.2
0.9
0.5
0.9
–
–
–
0.030
0.012
309.0 (16)
Rh-DIPAMP/SiO2
Rh-MANDYPHOS/SiO2
Rh-BINAP/SiO2
307.1 (87); 309.0 (13)
307.1 (87); 309.0 (13)
307.1 (74); 308.8 (26)
307.0 (84); 309.0 (16)
133.0
–
–
–
–
0.9
0.4
0.9
0.3
0.042
0.013
0.030
0.006
–
–
–
–
–
–
Rh(+)-DIOP/SiO2
3.2. PPD hydrogenation
MANDYPHOS/SiO2, which did not contain any oxygenated functional
groups, but instead dimethyl amine functionality. The low GCLPA is
due to strong adsorption of PPD or products on the catalyst surface.
Interestingly, it was observed in catalyst recycling that the GCLPA le-
vels increased indicating some changes in the ligand, although the
enantiomeric excess was retained (See Catalyst Recycling section).
The kinetic profiles for PPD hydrogenation over different catalysts
are shown in Figs. 5–9 and discussed for each catalyst separately.
Thereafter, the yield of the desired product (R)-1-hydroxy-1-phenyl-
propan-2-one was correlated with the metal particles size.
Supported Rh NPs stabilized by ligands were studied as chiral cat-
alysts in the PPD enantioselective reaction (Scheme 1). PPD is a very
important substrate and the main product in its hydrogenation, (R)-1-
hydroxy-1-phenylpropan-2-one acts as an intermediate for production
of L-ephedrine [66]. Many compounds can be obtained from hydro-
genation of PPD as reported in the literature [3,22–31] presenting also
the values of rate constants.
The initial TOFs obtained for PPD hydrogenation using supported
Rh NPs stabilized by different ligands (Table 3) diminished in the fol-
lowing order: Rh(-)-DIOP/SiO2 > Rh(+)-DIOP/SiO2 > Rh-TANIAP-
HOS/SiO2 = Rh-MANDYPHOS/SiO2 > > Rh-DIPAMP/SiO2. This ten-
dency is not directly correlated with the metal dispersion or the amount
of metal on the surface (Table 1, Table 2). For Rh-BINAP/SiO2 the in-
itial TOF after 10 min was not calculated due to an induction time of
20 min (Fig. 4). Thereafter PPD disappeared nearly completely from the
liquid phase due to strong interactions with the catalyst. This catalyst
contained also the lowest amount of metallic Rh (Table 3). On the other
hand, even if Rh-DIPAMP/SiO2 exhibited the smallest metal size and
also more ligand on the surface confirmed by XPS (P 2p at 133 eV)
compared to the other catalysts, it gave the lowest initial TOF.
Conversion of PPD decreased in the following order: Rh-BINAP/
SiO2 > Rh(-)-DIOP nanoparticles > Rh(-)-DIOP/SiO2 (Fig. 4). Rh-
BINAP/SiO2 gave also the lowest GCLPA (defined as the sum of con-
centrations of reactant and products visible in GC analysis), which is in
accordance with XPS results showing that a large amount of ligand is
present on the surface (Table 2). Low GCLPA levels were obtained both
for Rh-(-)DIOP nanoparticles and for Rh-(-)DIOP/SiO2 and the highest
values were determined for Rh-TANIAPHOS/SiO2 and for
The kinetic data for PPD hydrogenation over Rh-(-)-DIOP nano-
particles (Fig. 5a) showed that the transformation of PPD is initially
rather fast during the first 100 min. The total concentration (i.e. sum of
the reactant and product concentrations visible in GC analysis) declines
also 150 fold more rapidly during first 30 min than during 30–220 min
of the reaction (Fig. 5a). Thereafter the GCLPA declined even more
slowly. This result indicates that the reactant and products are strongly
adsorbed on the surface of catalyst particles. The maximum yield of the
main product, (R)-1-hydroxy-1-phenylpropan-2-one is ca. 17% at
150 min, after which its concentration declined, while the concentra-
tion of S-enantiomer is increasing with increasing time. Interestingly
GCLPA remains stable after 240 min. The ee1 increased more rapidly
than ee2 at high conversion levels (Fig. 5b) although no diols are
formed. This indicates that further transformations of R-enantiomer
giving oligomers there was an increase in the enantiomeric excess, ee1
with conversion. (R)-1-hydroxy-1-phenylpropan-2-one is thus more
reactive than the corresponding S-enantiomer in such reactions leading
to catalyst deactivation. The formed adsorbed species or oligomers
could not be identified by GC analysis.
The regioselectivity also declined with increasing conversion
Fig. 3. Binding energies (eV) of internal levels of a) unsupported Rh NPs and b) supported catalysts prepared from [Rh(μ−OCH3)(C8H12)]2 precursor.
5

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Table 3
Initial turn over frequency (TOF) (ee1, ee2 and rs at 70% conversion level for PPD hydrogenation over supported NPs obtained by stabilization with chiral ligands.
Reaction conditions: PPD concentration 0.02 mol L−1, (PPD/Rh) molar ratio: 100, 25 °C, 40 bar H2, stirring rate: 800 rpm, solvent: 50 mL of cyclohexane.
Catalysta
TOFb
(s−1
Conv.c (%)
GCLPAc (%)
Yield of R-1 (%)d
ee1 (%)
ee2 (%)
rsd
d
d
)
Rh(-)-DIOP nanoparticles
Rh(-)-DIOP/SiO2
Rh(+)-DIOP/SiO2
Rh-TANIAPHOS/SiO2
Rh-DIPAMP/SiO2
Rh-MANDYPHOS/SiO2
97
96
90
72e
80
90
16
23
55
75e
35
50
10
23
23
37
13
25
43
48
44
40
40
29
56
42
62
68
62
58
2
4
2
14
12
19
0.038
0.034
0.016
0.0033
0.016
a
1 wt.% Rh-Ligand/SiO2 catalysts from [Rh(μ−OCH3)(C8H12)]2 precursor.
initial TOF during the first 10 min, calculated as mole converted per mole Rh in second.
Conversion and GCLPA at 300 min of reaction.
at 70% conversion.
b
c
d
e
at 230 min.
low, there are more chances for PPD adsorption by C]O (2) [28].
For Rh-(+)-DIOP/SiO2 the kinetic profiles are shown in Fig. 6. In-
terestingly, in this case the GCLPA remained quite high, being 55%
after 300 min, while for Rh(-)-DIOP/SiO2 it was much lower. This result
indicates that chirality of the ligand has an effect on GCLPA and on the
interactions of the reactant and products with the surface. The yield of
the main product, (R)-1-hydroxy-1-phenylpropan-2-one (Fig. 6a) was
also rather high, 30% at 240 min and its concentration profile remained
relatively constant after 70 min opposite to Rh-(-)DIOP/SiO2. En-
antioselectivity ee1 increased with conversion, while ee2 was not in-
creasing after prolonged times (Fig. 6b). Regioselectivity exhibited a
similar declining trend as for Rh(-)DIOP/SiO2, although being only half
the one obtained by Rh(-)-DIOP/SiO2 (Table 3). This is due to the high
concentration of (R)-1-hydroxy-1-phenylpropan-2-one even at the end
of the experiment opposite to the case for Rh-(-)-DIOP/SiO2. The main
difference between these two catalysts was that Rh(-)DIOP/SiO2 ex-
hibited 3 fold more Rh on its surface in comparison to Rh(+)DIOP/SiO2
(Table 2).
For Rh-DIPAMP/SiO2 an induction period can be seen in Fig. 7a.
Finally, this catalyst provided the second lowest conversion of PPD after
300 min after Rh-TANIAPHOS/SiO2 (Table 3) despite its high metal
dispersion. The ee values were, however, with Rh-DIPAMP/SiO2 on the
same level (Fig. 6b) as for Rh-TANIAPHOS/SiO2 (Table 3). It should be
pointed out here, that the yield of the desired product is even more
important than ee, especially for the cases where reaction proceeded
slowly, e.g. Rh-DIPAMP/SiO2 and thus an overall comparison of the
yield of (R)-1-hydroxy-1-phenylpropan-2-one as a function of metal
particle size is presented at the end of this section.
Fig. 4. Evolution of PPD conversion with reaction time for catalysts synthesized
from [Rh(μ−OCH3)(C8H12)]2 with different ligands. Reaction conditions: PPD
concentration 0.02 mol L−1, molar ratio PPD/Rh: 100/1, stirring rate: 800 rpm,
25 °C, 40 bar H2, solvent: 50 mL of cyclohexane. Notation: Rh-(-)-DIOP nano-
particles (+), Rh-(-)-DIOP/SiO2 (♦), Rh-(+)-DIOP/SiO2 (◊), Rh-BINAP/SiO2
(Δ), Rh-TANIAPHOS/SiO2 (▲), Rh-DIPAMP/SiO2 (□) and Rh-MANDYPHOS/
SiO2 (o).
(Fig. 5b). The preferred carbonyl to be hydrogenated was the adjacent
to the phenyl group in PPD as reported in [28]. The reason for the high
regioselectivity towards hydrogenation, especially at the beginning of
the experiment is that C]O (1) is in the same plane as the phenyl ring.
Furthermore, it has been shown by quantum chemical calculations
using B3LYP, HF and MP2 methods that the C]O bond at C1 is weaker
than at C2. At high conversion levels when the concentration of PPD is
The GCLPA levels were very high for the two ligand-modified sup-
ported Rh catalysts containing dimethylamine group, namely
Rh-MANDYPHOS/SiO2 and Rh-TANIAPHOS/SiO2 (Fig. 8 and 9). Both
of these ligands contain not only amino groups, but also metallocene
Fig. 5. a) Evolution of PPD and products con-
centration (Notation: Sum of concentrations
(◼), PPD (+), (R)-1-hydroxy-1-phenylpropan-
2-one (▲) and (S)-2-hydroxy-1-phenylpropan-
1-one (o), (R)-1-hydroxy-1-phenylpropan-2-
one (▲) and (S)-2-hydroxy-1-phenylpropan-1-
one (Δ) with reaction time and b) ee1 (●) ee2
(o) and regioselectivity (◼) as a function of
conversion over Rh(-)-DIOP nanoparticles.
Reaction conditions: PPD concentration
0.02 mol L−1
, molar ratio (PPD/Rh): 100,
stirring rate: 800 rpm, 25 °C, 40 bar H2, sol-
vent: 50 mL of cyclohexane.
6

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Fig. 6. a) Evolution of PPD and products con-
centration (Notation: Sum of concentrations
(◼), PPD (+), (R)-1-hydroxy-1-phenylpropan-
2-one (●) and (S)-2-hydroxy-1-phenylpropan-
1-one (o), (R)-2-hydroxy-1-phenylpropan-1-
one (▲) and (S)-2-hydroxy-1-phenylpropan-1-
one (Δ) with reaction time and b) ee1 (●) ee2
(o) and regioselectivity (◼) as a function of
conversion over Rh(+)-DIOP/SiO2. Reaction
conditions: PPD concentration 0.02 mol L−1
,
molar ratio (PPD/Rh): 100, stirring rate:
800 rpm, 25 °C, 40 bar H2, solvent: 50 mL of
cyclohexane.
Fig. 7. a) Evolution of PPD and products con-
centration (Notation: Sum of concentrations
(◼), PPD (+), (R)-1-hydroxy-1-phenylpropan-
2-one (●), (S)-1-hydroxy-1-phenylpropan-2-
one (o), (R)-2-hydroxy-1-phenylpropan-1-one
(▲) and (S)-2-hydroxy-1-phenylpropan-1-one
(Δ) with reaction time and b) ee1 (●) ee2 (o)
and regioselectivity (◼) as a function of con-
version over Rh-DIPAMP/SiO2. Reaction con-
ditions: PPD concentration 0.02 mol L−1
,
molar ratio (PPD/Rh): 100, stirring rate:
800 rpm, 25 °C, 40 bar H2, solvent: 50 mL of
cyclohexane.
Fig. 8. a) Evolution of PPD and products con-
centration (Notation: Sum of concentrations
(◼), PPD (+), (R)-1-hydroxy-1-phenylpropan-
2-one (●) and (S)-1-hydroxy-1-phenylpropan-
2-one (o), (R)-2-hydroxy-1-phenylpropan-1-
one (▲) and (S)-2-hydroxy-1-phenylpropan-1-
one (Δ) with reaction time and b) ee1 (●) ee2
(o) and regioselectivity (◼) as a function of
conversion over Rh(+)-MANDYPHOS/SiO2.
Reaction conditions: PPD concentration
0.02 mol L−1
, molar ratio (PPD/Rh): 100,
stirring rate: 800 rpm, 25 °C, 40 bar H2, sol-
vent: 50 mL of cyclohexane.
Fig. 9. Evolution of PPD and products con-
centration (Notation: Sum of concentrations
(◼), PPD (+), (R)-1-hydroxy-1-phenylpropan-
2-one (●), (S)-1-hydroxy-1-phenylpropan-2-
one (o), (R)-2-hydroxy-1-phenylpropan-1-one
(▲) and (S)-2-hydroxy-1-phenylpropan-1-one
(Δ) with reaction time and b) ee1 (●) ee2 (o)
and regioselectivity (◼) as a function of con-
version over Rh-TANIAPHOS/SiO2. Reaction
conditions: PPD concentration 0.02 mol L−1
,
molar ratio (PPD/Rh): 100, stirring rate:
800 rpm, 25 °C, 40 bar H2, solvent: 50 mL of
cyclohexane.
(ferrocene), which could decrease interactions with PPD and its pro-
ducts.
Over Rh-(+)MANDYPHOS/SiO2 and Rh-TANIAPHOS/SiO2 the
maximum yields of (R)-1-hydroxy-1-phenylpropan-2-one were 30%
Enantiomeric excesses for the main product, i.e. ee1 were about at the
same level as for Rh-(-)DIOP/SiO2, while regioselectivities for
Rh-MANDYPHOS/SiO2 and Rh-DIPAMP/SiO2 were much higher being
19 and 12 at 70% conversion than obtained for Rh-(-)DIOP/SiO2
(Table 3). This result clearly shows also that the ligand structure has an
and 50% at 240 min and 182 min, respectively (Fig. 8a,
9 a).
7

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
3.3. Catalyst recycling
One of the main objectives of this work was to study the reusability
of chiral Rh(-)-DIOP/SiO2 catalysts in PPD hydrogenation. The spent
catalyst was washed between the experiments with pentane and dried
in vacuum. The performance of the fresh and reused supported Rh
(-)-DIOP/SiO2 was compared with that of the unsupported Rh(-)-DIOP
nanoparticles (Table 5). It can be observed that the highest initial
transformation rate of PPD as well as the final conversion were ob-
tained for Rh-(-)-DIOP nanoparticles followed by fresh Rh-(-)-DIOP/
SiO2, once used and twice used and the GCLPA was inversely propor-
tional to the conversion level (Fig. 11a). The GCLPA indicates that the
interactions of the reactant and/ or products are the most prominent
with Rh-(-)-DIOP nanoparticles and less prominent for the reused cat-
alysts. The reused catalyst exhibited a lower reaction rate, but no clear
deactivation was observed and the final conversion with this catalyst
was 88%. The catalyst reused twice showed an analogous kinetic profile
as the once reused catalyst giving the conversion level of 76%. The
reason for the lower conversion levels obtained with the reused Rh
(-)-DIOP/SiO2 is a slight increase in the average Rh particle sizes,
confirmed by TEM analysis, as it was performed for the catalysts after
the reaction. The average Rh particle sizes for fresh, once used and
twice reused were 2.4, 2.9 and 3.2 nm, respectively.
Fig. 10. The average Rh particle size as a function of the yield of the main
product, (R)-1-hydroxy-1-phenylpropan-2-one at 70% conversion.
effect on product distribution. High regioselectivity obtained over
Rh-MANDYPHOS/SiO2 and Rh-DIPAMP/SiO2 indicates that it is more
challenging for C = O at position C2 to be in contact with Rh.
The highest yield of the desired product was obtained with
Rh-TANIAPHOS/SiO2 exhibiting an optimum metal particle size of
2 nm (Table 1), while e.g. Rh-DIPAMP/SiO2 with a smaller metal par-
ticle size gave only 13% yield of the desired product (Fig. 10). In en-
antioselective hydrogenation of (-)-cinchonidine modified Pt catalyst,
in which an optimum Pt particle size facilitated simultaneous adsorp-
tion and interaction of the modifier and the reactant on metal surface,
being, however, slightly larger than in the current case, i.e. 3.8 nm for
Pt/SiO2 [30]. The correlation with the fraction of Rh0 in XPS results
(Table 2) shows also that the lowest yield of (R)-1-hydroxy-1-phenyl-
propan-2-one at 70% conversion, i.e. 10%, was obtained with Rh-(-)
DIOP nanoparticles exhibiting only 76% of Rh in metallic state,
whereas Rh/TANIAPHOS/SiO2 with 80% Rh0 gave 37% yield.
When comparing the current results obtained by Rh-DIPAMP/SiO2,
R-TANIAPHOS/SiO2 and Rh(-)-DIOP/SiO2 with those reported in the
literature for PPD hydrogenation (Table 4), it can be observed that the
ee1 values obtained for ligand-Rh/SiO2 are rather high. The metal
particle sizes in ligand-Rh/SiO2 are small in comparison with the case,
in which (-)-cinchonidine was used as a modifier with Pt supported
catalysts, since cinchonidine adsorption requires a relatively large
metal particle. A small Rh particle size is an advantage helping to utilize
the metal surface. One of the main benefits with these ligand-Rh/SiO2
catalysts is that only mild conditions are required to reduce the metal
nanoparticle in the presence of ligand opposite to conventional Pt
supported catalysts, which should be reduced prior to the reaction at
high temperature [22–30].
The enantiomeric excess, on the other hand is slightly increasing
with recycling (Table 5, Fig. 11b). Interestingly the highest regios-
electivity was determined for once reused catalysts (Fig. 11b). These
results are promising, clearly showing that chirality is retained in the
reused catalysts.
4. Conclusions
Chiral metal supported catalysts stabilized by P-ligands have shown
promising behavior as heterogeneous catalysts for the enantioselective
hydrogenation of 1-phenyl-1,2-propanedione. Reduction of organome-
tallic Rh precursor in the presence of ligands under mild conditions
allowed to obtain clean chiral Rh surfaces that can be used more than
once without additional amounts of chiral inducer in situ. Differences in
activity and enantioselectivity have been discussed according to cata-
lytic properties and characterization data, obtained with XPS and HR-
TEM. An optimum Rh particle size of 2 nm over Rh-TANIAPHOS/SiO2
gave the highest yield of the desired product, 50% at 65% conversion.
Reuse of catalyst was investigated for silica supported [Rh
(μ−OCH3)(C8H12)]2 with (-)-DIOP. The yield of 1-hydroxy-1-phenyl-
propan-2-one at 70% conversion level remained in the range 23–25%
when the catalyst was reused, although the final conversion level de-
creased from 95% to 76% in 5 h during catalyst recycling. This result
indicates that Rh-(-)-DIOP/SiO2 catalyst can be successfully reused in
enantioselective hydrogenation of 1-phenyl-1,2-propanedione.
Table 4
Comparison of metal particle sizes and enantiomeric excesses in this work with literature data on PPD hydrogenation.
Catalyst
Metal particle size (nm)
Conditions
Conv. (%)
ee (%)
Ref.
5 wt% Pt/Al2O3
5 wt% Pt/SiO2
2.5
3.7
1.6
3.2
4.8
1.7
1.7
3.8
25 °C, 5 bar H2, ethyl acetate, CDa
25 °C, 5 bar H2, ethyl acetate, CDa
25 °C, 40 bar H2, cyclohexane
25 °C, 20 bar H2, cyclohexane
25 °C, 40 bar H2, cyclohexane
25 °C, 40 bar H2, cyclohexane
25 °C, 40 bar H2, cyclohexane
25 °C, 40 bar H2, cyclohexane
98
98
97
67
98
95
92
65
93
64
41
65
72
48
37
48
[29]
[30]
[33]
[63]
[19]
This work
[35]
Pt/SiO2-CD, grafted CD
1 wt % Rh-MCM-41-CD
Rh-(R,R)-BDPP/SiO2
1 wt% Rh(-)-DIOP/SiO2
1 wt% Pt/TNT-CDb, grafted CD
Pt(Pylm) /SiO2
[34]
a
CD means added cinchonidine as a modifier.
Titanate nanotubes.
b
8

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Table 5
The results from recycling of Rh-(-)-DIOP/SiO2 in PPD hydrogenation at 25 °C under 40 bar hydrogen. As a comparison the performance of Rh-(-)-DIOP nanoparticles
is also presented here. Reaction conditions: PPD concentration 0.02 mol L−1, (PPD/Rh) molar ratio: 100, 25 °C, 40 bar H2, stirring rate: 800 rpm, solvent: 50 mL of
cyclohexane. R-1 denotes (R)-1-hydroxy-1-phenylpropan-2-one.
a
b
c
c
c
Catalyst
GCLPA (%)
Conversion min (%)
Yield of R-1 (%)
ee1 (%)
ee2 (%)
rs
Rh(-)-DIOP Nanoparticles
fresh
Rh(-)-DIOP/SiO2
once reused
Rh(-)-DIOP/SiO2
twice reused
20
23
98
95
10
23
43
40
56
40
4
5.5
9
55
70
88
76
24
25
38
50
62
58
4
Rh(-)-DIOP/SiO2
a
after 240.
70% conversion.
at 50% conversion.
b
c
Acknowledgements
Authors would like to acknowledge financial support of CONICYT
through FONDECYT N° 1161660 project by financial support of this
work. C. Claver and C. Godard are grateful to the Ministerio de
Economia y Competividad and the Fondo Europeo de Desarrollo
Regional FEDER (CTQ2016-75016-R, AEI/FEDER,UE).
References
[1] P.M. Subramanian, S.K. Chatterjee, M.C. Bhatia, Synthesis of (1RS,
2SR)‐( )‐2‐amino‐1‐phenyl‐1-propanol from
(R)‐(−)‐1‐hydroxy‐1‐phenyl‐2‐propanone, J. Chem. Technol. Biot. 39 (4) (1987)
215–218.
[2] D. Gala, D.J. DiBenedetto, J.E. Clark, B.L. Murphy, D.P. Schumacher, M. Steinman,
Preparations of antifungal Sch 42427/SM 9164: preparative chromatographic re-
solution, and total asymmetric synthesis via enzymatic preparation of chiral α-
hydroxy arylketones, Tetrahedron Lett. 37 (5) (1996) 611–614.
[3] V.B. Shukla, P.R. Kulkarni, J. World, L-Phenylacetylcarbinol (L-PAC): biosynthesis
and industrial applications, Microbiol. Biotechnol. 16 (2000) 499–506.
[4] Y. Orito, S. Imai, S. Niwa, Asymmetric hydrogenation of methyl pyruvate using Pt-C
catalyst modified with cinchonidine, Nippon. Kagaku Kaishi 8 (1979) 1118–1120.
[5] Y. Orito, S. Imai, S. Niwa, G.H. Nguyen, Asymmetric hydrogenation of ethyl pyr-
uvate on Pt/Al2O3 catalyst used cinchonidine as modifier, J. Synth. Org. Chem. Jpn.
37 (1979) 173–176.
[6] D.Yu. Murzin, P. Mäki-Arvela, E. Toukoniitty, T. Salmi, Asymmetric heterogeneous
catalysis: science and engineering, Catal. Rev. Sci. Eng. 47 (2005) 175–256.
[7] P. Gallezot, D. Richard, Selective hydrogenation of α, β-unsaturated aldehydes,
Catal. Rev. 40 (1-2) (1998) 81–126.
[8] G. Szöllősi, S.I. Niwa, T.A. Hanaoka, F. Mizukami, Enantioselective hydrogenation
of α,β-unsaturated carboxylic acids over cinchonidine-modified Pd catalysts: effect
of substrate structure on the adsorption mode, J. Mol. Catal. A Chem. 230 (1)
(2005) 91–95.
[9] A. Roucoux, M. Devocelle, J.F. Carpentier, F. Agbossou, A. Mortreoux, Highly ef-
ficient asymmetric hydrogenation of activated and unactivated ketones catalyzed
by Rhodium(I) aminophosphine and amidophosphine phosphinite complexes,
Beneficial Effect of the Non Chiral Ligand, Synlett. 4 (1995) 358–360.
[10] J.L. Margitfalvi, E. Tálas, Enantioselective hydrogenation of ethyl pyruvate over
cinchonidine–Pt/Al2O3 catalysts containing anchored silicium organic moieties,
Appl. Catal. A Gen. 182 (1) (1999) 65–74.
[11] K. Borszeky, T. Mallat, A. Baiker, Enantioselective hydrogenation of α, β-un-
saturated acids. Substrate-modifier interaction over cinchonidine modified
PdAl2O3, Tetrahedron Asymmetry 8 (22) (1997) 3745–3753.
[12] D.J. Ager, A.H. Vries, J.G. Vries, Asymmetric homogeneous hydrogenations at scale,
Chem. Soc. Rev. 41 (8) (2012) 3340–3380.
[13] Q.A. Chen, Z.S. Ye, Y. Duan, Y.G. Zhou, Homogeneous palladium-catalyzed asym-
metric hydrogenation, Chem. Soc. Rev. 42 (2) (2013) 497–511.
[14] P. McMorn, G.J. Hutchings, Heterogeneous enantioselective catalysts: strategies for
the immobilisation of homogeneous catalysts, Chem. Soc. Rev. 33 (2) (2004)
108–122.
[15] W. Tang, X. Zhang, New chiral phosphorus ligands for enantioselective hydro-
genation, Chem. Rev. 103 (8) (2003) 3029–3070.
[16] A. Choplin, F. Quignard, From supported homogeneous catalysts to heterogeneous
molecular catalysts, Coord. Chem. Rev. 178 (1998) 1679–1702.
[17] G. Szöllősi, A. Mastalir, Z. Kiraly, I. Dekany, Preparation of Pt nanoparticles in the
presence of a chiral modifier and catalytic applications in chemoselective and
asymmetric hydrogenations, J. Mater. Chem. 15 (25) (2005) 2464–2469.
[18] C. Mella, M. Avila, A. Sanchez, T. Marzialetti, P. Reyes, D. Ruiz, Chiral Rh/SiO2
catalysts for enantioselective hydrogenation reactions: the role of (S,S)-DIPAMP as
chiral modifier and stabilizer on metallic nanoparticles synthesis, J. Chil. Chem.
Soc. 58 (4) (2013) 2125–2130.
Fig. 11. a) Conversion (open symbol) and normalized total concentration of
reactant (%, solid symbol) and products as a function of time, b) ee1 (solid
symbol) ee2 (open symbol) and c) regioselectivity as a function of conversion in
enantioselective hydrogenation of PPD over Rh-DIOP/SiO2 at 25 °C under
40 bar in hydrogen. Symbols: fresh catalyst (●), reused once (▲) and reused
twice (◼), open symbol denotes conversion and closed symbol normalized total
liquid phase concentration determined by GC.
[19] D. Ruiz, M. Oportus, C. Godard, C. Claver, J.L.G. Fierro, P. Reyes, Novel Metal
9

D. Ruiz, et al.
MolecularCatalysis477(2019)110551
Nanoparticles Stabilized with (2R,4R)-2, 4-bis (diphenylphosphino)pentane on
catalyst, Eur. J. Clin. Chem. Clin. Biochem. 3 (1997) 1200–1202.
SiO2. Their Use as Catalysts in Enantioselective Hydrogenation Reactions, Curr.
Org. Chem. 16 (23) (2012) 2754–2762.
[43] P. Barbaro, V. Dal Santo, F. Liguori, Emerging strategies in sustainable fine-che-
mical synthesis: asymmetric catalysis by metal nanoparticles, Dalton Trans. 39 (36)
(2010) 8391–8402.
[44] M.J. Jacinto, P.K. Kiyohara, S.H. Masunaga, R.F. Jardim, L.M. Rossi, Recoverable
rhodium nanoparticles: synthesis, characterization and catalytic performance in
hydrogenation reactions, Appl. Catal. A Gen. 338 (1) (2008) 52–57.
[45] J. Koktan, H. Sedláčková, I. Osante, C. Cativiela, D.D. Díaz, P. Řezanka, Chiral
supramolecular nanoparticles: the study of chiral surface modification of silver
nanoparticles by cysteine and its derivatives, Colloids Surf. A Physicochem. Eng.
Asp. 470 (2015) 142–148.
[46] A. Roucoux, Stabilized Noble Metal Nanoparticles: an unavoidable family of cata-
lysts for arene derivative hydrogenation, Top. Organomet. Chem. 16 (2005)
261–279.
[47] M. Axet, S. Castillón, C. Claver, K. Philippot, P. Lecante, B. Chaudret, Chiral di-
phosphite-modified Rhodium(0) nanoparticles: catalyst reservoir for styrene hy-
droformylation, Eur. J. Inorg. Chem. 22 (2008) 3460–3466.
[48] S. Jansat, M. Gomez, K. Philippot, G. Muller, E. Guiu, C. Claver, S. Castillon,
B.A. Chaudret, Case for enantioselective allylic alkylation catalyzed by palladium
nanoparticles, J. Am. Chem. Soc. 126 (2004) 1592–1593.
[49] S. Castillon, C. Claver, Y. Diaz, C1 and C2-symmetric carbohydrate phosphorus li-
gands in asymmetric catalysis, Chem. Soc. Rev. 34 (8) (2005) 702–713.
[50] H.J. Zhu, Y.J. Ding, L. Yan, J.M. Xiong, Y. Lu, L.W. Lin, The PPh 3 ligand modified
Rh/SiO2 catalyst for hydroformylation of olefins, Catal. Today 93 (2004) 389–393.
[51] E. Ramirez, S. Jansat, K. Philippot, P. Lecante, M. Gomez, A.M. Masdeu-Bultó,
B. Chaudret, Influence of organic ligands on the stabilization of palladium nano-
particles, J. Organomet. Chem. 689 (24) (2004) 4601–4610.
[52] S.U. Son, Y. Jang, K.Y. Yoon, E. Kang, T. Hyeon, Facile synthesis of various phos-
phine-stabilized monodisperse palladium nanoparticles through the understanding
of coordination chemistry of the nanoparticles, Nano Lett. 4 (6) (2004) 1147–1151.
[53] B. Léger, A. Denicourt-Nowicki, H. Olivier-Bourbigou, A. Roucoux, Rhodium na-
nocatalysts stabilized by various bipyridine ligands in nonaqueous ionic liquids:
influence of the bipyridine coordination modes in arene catalytic hydrogenation,
Inorg. Chem. 47 (19) (2008) 9090–9096.
[54] A. Gual, M.R. Axet, K. Philippot, B. Chaudret, A. Denicourt-Nowicki, A. Roucoux,
S. Castillón, C. Claver, Diphosphite ligands derived from carbohydrates as stabi-
lizers for ruthenium nanoparticles: promising catalytic systems in arene hydro-
genation, Chem. Commun. (Camb.) (2008) 2759–2761.
[20] R. Somanathan, N.A. Cortez, M. Parra-Hake, D. Chávez, G. Aguirre, Immobilized
chiral metal catalysts for enantioselective hydrogenation of ketones, Mini. Org.
Chem. 5 (4) (2008) 313–322.
[21] C. Bianchini, P. Barbaro, Recent aspects of asymmetric catalysis by immobilized
chiral metal catalysts, Top. Catal. 19 (1) (2002) 17–32.
[22] E. Toukoniitty, P. Mäki-Arvela, N. Kumar, T. Salmi, D.Y. Murzin, Continuous en-
antioselective hydrogenation of ethyl benzoylformate over Pt/Al2O3 catalyst: bed
dilution effects and cinchonidine adsorption study, Catal. Lett. 95 (2004) 179–183.
[23] E. Toukoniitty, P. Mäki-Arvela, M. Kuzma, D.Yu. Murzin, Enantioselective hydro-
genation of 1-phenyl-1,2-propanedione, J. Catal. 204 (2001) 281–291.
[24] E. Toukoniitty, P. Mäki-Arvela, A.N. Villela, P.J. Kooyman, The effect of oxygen and
the reduction temperature of the Pt/Al2O3 catalyst in enantioselective hydrogena-
tion of 1-phenyl-1,2-propanedione, Catal. Today 60 (2000) 175–184.
[25] E. Toukoniitty, J. Wärnå, P. Mäki-Arvela, T. Salmi, D.Yu. Murzin, Application of
transient methods in three-phase catalysis: hydrogenation of a dione in a catalytic
plate column, Catal. Today 383 (2003) 79–80.
[26] E. Toukoniitty, P. Mäki-Arvela, A. Kalantar Neyestanaki, T. Salmi, D.Y. Murzin,
Continuous hydrogenation of 1-phenyl-1,2-propanedione under transient and
steady-state conditions: regioselectivity, enantioselectivity and catalyst deactiva-
tion, Appl. Catal. A Gen. 235 (2002) 125–138.
[27] E. Toukoniitty, P. Mäki-Arvela, N. Kumar, T. Salmi, D.Y. Murzin, Influence of mass
transfer on regio- and enantioselectivity in hydrogenation of 1-phenyl-1,2-propa-
nedione over modified Pt catalysts, Catal. Today 79–80 (2003) 189–193.
[28] E. Toukoniitty, P. Mäki-Arvela, V. Nieminen, M. Hotokka, J. Päivärinta, T. Salmi,
D.Y. Murzin, Enhanced Regioselectivity in Batch and Continuous Hydrogenation of
1-phenyl-1,2-propanedione Over Modified Pt Catalysts, Catalysis of Organic
Reactions, Marcel Dekker (Ed), New York, 2002, pp. 341–358.
[29] E. Toukoniitty, P. Mäki-Arvela, J. Wärnå, T. Salmi, Modeling of the enantioselective
hydrogenation of 1-phenyl-1,2-propanedione over Pt/Al2O3, Catal. Today 66 (2–4)
(2001) 411–417.
[30] E. Toukoniitty, P. Mäki-Arvela, A. Kalantar Neyestanaki, T. Salmi, R. Sjöholm,
R. Leino, E. Laine, P. Kooyman, T. Ollonqvist, T. Väyrynen, Batchwise and con-
tinuous enantioselective hydrogenation of 1-phenyl-1,2-propanedione catalysed by
new Pt/SiO2 fibres, Appl. Catal. A Gen. 216 (2001) 73–83.
[31] C. Urbina, C. Campos, G. Pecchi, C. Claver, P. Reyes, Chiral Pt/ZrO2 catalysts.
Enantioselective hydrogenation of 1-phenyl-1,2-propanedione, Molecules 15
(2010) 3428–3440.
[32] D. Ruiz, C. Mella, J.L.G. Fierro, P. Reyes, Silica supported rhodium metal nano-
particles stabilized with (-)-DIOP. Effect of ligand concentration and metal loading
on the enantioselective hydrogenation of ketones, J. Chil. Chem. Soc. 57 (4) (2012)
1394–1399.
[33] D. Ruiz, J.L.G. Fierro, P. Reyes, Enantioselective hydrogenation of ethyl pyruvate
and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal
platinum on SiO2, J. Braz. Chem. Soc. 21 (2) (2010) 262–269.
[34] C.H. Campos, C.C. Torres, A. Leyton, J. Belmar, C. Mella, P. Osorio-Vargas, D. Ruiz,
J.L.G. Fierro, P. Reyes, A new non-cinchona chiral modifier immobilized on Pt/SiO2
catalysts for enantioselective heterogeneous hydrogenation, Appl. Catal. A Gen. 498
(2015) 76–87.
[55] D. Han, X. Li, H. Zhang, Z. Liu, G. Hu, C. Li, Asymmetric hydroformylation of olefins
catalyzed by rhodium nanoparticles chirally stabilized with (R)-BINAP ligand, J.
Mol. Cat. A. Chem. 283 (2008) 15–22.
[56] A. Gual, C. Godard, K. Philippot, B. Chaudret, A. Denicourt‐Nowicki, A. Roucoux,
C. Claver, Carbohydrate‐derived 1,3‐diphosphite ligands as chiral nanoparticle
stabilizers: promising catalytic systems for asymmetric hydrogenation,
ChemSusChem. 2 (8) (2009) 769–779.
[57] C.W. Chen, T. Serizawa, M. Akashi, Preparation of platinum colloids on polystyrene
nanospheres and their catalytic properties in hydrogenation, Chem. Mater. 11 (5)
(1999) 1381–1389.
[58] A.B. Lowe, B.S. Sumerlin, M.S. Donovan, C.L. McCormick, Facile preparation of
transition metal nanoparticles stabilized by well-defined (co) polymers synthesized
via aqueous reversible addition-fragmentation chain transfer polymerization, J.
Am. Chem. Soc. 124 (39) (2002) 11562–11563.
[35] C.H. Campos, C.C. Torres, P. Osorio-Vargas, C. Mella, J. Belmar, D. Ruiz,
J.L.G. Fierro, P. Reyes, Immobilized chiral inducer on Pt-based mesoporous titanate
nanotubes as heterogeneous catalysts for enantioselective hydrogenation, J. Mol.
Catal. A Chem. 398 (2015) 190–202.
[59] S.A. Stratton, K.L. Luska, A. Moores, Rhodium nanoparticles stabilized with phos-
phine functionalized imidazolium ionic liquids as recyclable arene hydrogenation
catalysts, Catal. Today 183 (1) (2012) 96–100.
[36] A. Lindholm, P. Mäki-Arvela, E. Toukoniitty, T. Salmi, D.Y. Murzin, R. Sjöholm,
R. Leino, Hydrosilylation of cinchonidine and 9-O-TMS-cinchonidine with trie-
thoxysilane: application of 11-(triethoxysilyl)-10,11-dihydrocinchonidine as a
chiral modifier in the enantioselective hydrogenation of 1-phenyl-1,2-propane-
dione, Perkin Transactions I (2002) 2605–2612.
[37] Y. Huang, J. Chen, H. Chen, R. Li, Y. Li, L. Min, X. Li, Enantioselective hydro-
genation of ethyl pyruvate catalyzed by PVP-stabilized rhodium nanoclusters, J.
Mol. Catal. A Chem. 170 (2001) 143–146.
[38] V. Mévellec, A. Nowicki, A. Roucoux, C. Dujardin, P. Granger, E. Payen,
K. Philippot, A simple and reproducible method for the synthesis of silica-supported
rhodium nanoparticles and their investigation in the hydrogenation of aromatic
compounds, New J. Chem. 30 (2006) 1214–1219.
[60] D. Han, X. Li, H. Zhang, Z. Liu, J. Li, C. Li, Heterogeneous asymmetric hydro-
formylation of olefins on chirally modified Rh/SiO2 catalysts, J. Catal. 243 (2006)
318–328.
[61] M.L. Tschan, O. Diebolt, P.W.N.M. van Leeuwen, Ruthenium metal nanoparticles in
hydrogenation: influence of phosphorus-ligands, Top. Catal. 57 (10-13) (2014)
1054–1065.
[62] T. Marzialetti, M. Oportus, D. Ruiz, J.L.G. Fierro, P. Reyes, Enantioselective hy-
drogenation of 1-phenyl-1,2-propanedione, ethyl pyruvate and acetophenone on Ir/
SiO2 catalysts: effect of iridium loading, Catal. Today 133 (2008) 711–719.
[63] C.C. Torres, C.H. Campos, J.L.G. Fierro, P. Reyes, D. Ruiz, Enantioselective hy-
drogenation of 1-phenyl-1,2-propanedione on cinchonidine-modified Rh/MCM-41
catalysts, J. Mol. Catal. A Chem. 392 (2014) 321–328.
[39] A. Roucoux, J. Schulz, H. Patin, Reduced Transition Metal Colloids. A Novel Family
of Reusable Catalysts, Chem. Rev. 102 (2002) 3757–3778.
[64] J. Chatt, L.M. Venanzi, Olefin coordination compounds. Diene complexes of rho-
dium(I), J. Chem. Soc. (1957) 4735–4741.
[40] H. Bönnemann, G.A. Braun, Enantioselective hydrogenations on platinum colloids,
Angew. Chem. Int. Ed. Engl. 35 (17) (1996) 1992–1995.
[41] B. Chaudret, Organometallic approach to nanoparticles synthesis and self-organi-
[65] R. Uson, L.A. Oro, J.A. Cabeza, Dinuclear methoxy, cyclooctadiene, and barrelene.
Complexes of Rhodium(I) and Iridium(I), Inorg. Synth. 23 (1985) 126–130.
[66] V.B. Shukala, P.R. Kulkarni, L-phenylacetlcarbinol (L-PAC): biosynthesis and in-
dustrial applications, World J. Microbiol. Biotechnol. 16 (2000) 499–506.
zation, C. R. Phys. 6 (2005) 117–131.
[42] H. Bönnemann, G.A. Braun, Enantioselectivity control with metal colloids as
10