Chiral rh/sio2 catalysts for enantioselective Hydrogenation reactions. the role of (S,S)-dipamp as chiral modifier and Stabilizer on metallic nanoparticles Synthesis

Article abstract of DOI:10.4067/S0717-97072013000400050

Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO2 prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochiral compounds. The catalysts synthesized from [Rh(?-OMe)(COD)]2 in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal dispersion. As shown by TEM, the metal particle size ranged between 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. (S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as 25 C, 40 bar of H2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric excess (ee) levels up to 99% and 54% respectively.

Full text of DOI:10.4067/S0717-97072013000400050

J. Chil. Chem. Soc., 58, Nº 4 (2013)
CHIRAL Rh/SiO2 CATALYSTS FOR ENANTIOSELECTIVE HYDROGENATION REACTIONS. THE ROLE OF
(S,S)-DIPAMPAS CHIRAL MODIFIER AND STABILIZER ON METALLIC NANOPARTICLES SYNTHESIS
CLAUDIO MELLA1, MAURICIO ÁVILA1, ARIEL SÁNCHEZ1, TERESITA MARZIALETTI2,
PATRICIO REYES1 AND DORIS RUIZ1*.
1Universidad de Concepción, Facultad Ciencias Químicas, Edmundo Larenas 129, Concepción, Chile. Phone: (+056)41 2204324, Fax: (+056)41 2245974.
2 Universidad de Concepción, Departamento Ingeniería Química, Barrio Universitario S/No, Concepción, Chile
(Received: August 19, 2013-Accepted: november 29, 2013)
ABSTRACT
Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO
prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochira2l
compounds. The catalysts synthesized from [Rh(μ-OMe)(COD)] in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal
dispersion. As shown by TEM, the metal particle size ranged betw2een 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques
were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N2 adsorption-desorption
isotherms.
(S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity
in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as
25 °C, 40 bar of H2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric
excess (ee) levels up to 99% and 54% respectively.
Keywords: (S,S)-DIPAMP, stabilized nanoparticles, enantioselective hydrogenation, rhodium, chiral ligand.
INTRODUCTION
Nowadays, catalysis is one of the most essential research areas of metal
nanoparticles1-3. Controlled sized metal nanoparticles (NPs) have received
considerable attention due to their high surface area compared to bulk catalytic
materials4-5. Metal agglomeration is an undesired process, mainly in catalytic
reactions, because it leads to loss some properties associated with the “nano
state”. Chiral stabilizer agents control metal growing generating high amount
of metal particles on the asymmetry surface6-13. One of the strategies to take
advantage of the abilities of the stabilizer agents and use them for catalytic
applications is the deposition of chiral nanostructured metal colloids on catalyst
supports such as SiO2 and other mesoporous materials. Chiral modification
of metal surfaces has expanding successfully the powerful potential of
heterogeneous metal catalysts14-15. One of the most successful reactions in
Figure1.Chemicalstructureofa)(S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)
phenylphosphine] ligand, b) di-µ-methoxybis(1,5-cyclooctadiene) dirhodium
this area is the asymmetric hydrogenation of α, β-keto esters and ketones16.
Synthesis of enantiopure alcohols is of vital importance in pharmaceutical and
as precursor, and c) ethyl pyruvate, d) ketopantolactone, e) 3,4-hexanodione
flavoring industries17-18
. Alcohols are commonly synthesized by metal NPs
and f) acetophenone as prochiral substrates.
such as Rh, Ru, Ir and Pt. A few research groups have focused their studies in
using chiral nanoparticles as catalysts. NPs have been also used as catalysts in
reactions such as hydroformylation, allylic alkylation, hydrosilylations, Suzuki
Acetophenone (99.0%, 1.03 g mL-1), was purchased from Fluka and
distilled prior reactions.
and Heck-type, couplings, among others achieving good results19-26
.
Ketopantolactone (97%), 3,4-hexanodione (95%, 0.939 g mL-1), pentane,
tetrahydrofuran and dichloromethane (all of them from Aldrich), chloroform,
cyclohexane, methanol, diethylether and ethanol (96%), all from Merck, were
distilled prior reactions. THF was treated by metallic sodium. Precursors and
catalysts were prepared under purified N atmosphere.
Considering previous statements, both composition of NPs and prevention
of particle aggregation of immobilized systems are critical features required by
heterogeneous catalysts to be used in enantiomeric reactions.
This paper report the effective performance of a synthesized catalysts
N2 and H (99.995% of purity) wer2e purchased from Linde. SiO2 BASF
was heated at 2150 °C for 2 h before use to remove surface residues.
Chemical structure of keys compounds used in this work, such as the
chiral ligand, organometallic precursor and substrates are shown in Figure 1.
having rhodium nanoparticles supported on SiO214,15,27
.
The catalysts were synthesized by reducing an olefin and ligand
displacement from organometallic precursor in the presence of (S,S)-DIPAMP
(see Fig. 1) and SiO2 on H2. Adding different amounts of a chiral ligand
controls the metal average diameters, increasing specific metal surface area,
metal dispersion and also obtaining asymmetric heterogeneous catalysts useful
in enantioselective hydrogenation of HD, EP, KP and AP, as shown in figure 1.
Synthesis of organometallic precursor
The organometallic precursor [Rh(μ-OMe)(COD)]2 was prepared from
Rh(μ-Cl)(COD)]2.
All products of these reactions have applications in chiral drugs syntheses28-35
.
Rh(μ-Cl)(COD)] was synthesized from RhCl ·3H2O (0.5 g, 2.0 mmol)
and 1.1 mL of COD i2n 20 mL of ethanol were stirre3d under reflux at 70 °C for
3 hours obtaining a yellow precipitate (eq. 1). It was filtered and washed with
cold diethyl ether at 5 ºC collecting 71% of total solid. The following reaction
is taking place during preparation.
EXPERIMENTAL
Unless noted otherwise, all experiments were carried out using standard
Schlenk and vacuum-lines. Substrates and solvents used in this study were
analytical grade and treated by standard methods1,23,24
Materials
.
2RhCl + 2COD + 2CH3CH2OH → [Rh(μ-Cl)(COD)]2 + 4HCl +
2CH3CHO3 ( eq. 1)
RhCl3·3H2O, ethyl pyruvate (98%, 1.045
cyclooctadiene (COD) ≥95%, (S,S)-DIPAMP (≥95%) and KOH (≥85%) were
g
mL-1), cis,cis-1,5-
used as received from Aldrich without further purification.
Finally, [Rh(μ-Cl)(COD)]2 (175 mg, 0.36 mmol) dissolved in
e-mail: doruiz@udec.cl.
2125

J. Chil. Chem. Soc., 58, Nº 4 (2013)
dichloromethane (15 mL) was added to a solution of KOH (40 mg, 0.71 mmol)
in methanol (5 mL). Immediately a dark yellow solid, [Rh(μ-OMe)(COD)]2
see eq. 2, precipitates. After 30 minutes of stirring at room temperature, the
solvent was removed under vacuum. Yellow precipitate was mixed with 10 mL
of methanol and 15 mL of water. Then, the solution was filtered, washed (H O,
3x5 mL) and finally under dried vacuum without further purification. The yi2eld
of this step was 75%. The reaction controlling this step is represented below:
samples. As expected, these observations connected stabilizing properties of
the (S,S)-DIPAMP ligand with the control of the agglomeration of supported
nanoparticles, making this procedure a useful, easy and reproducible method of
preparing materials for catalytic purposes1,13,15
.
Table 1. Average particle size (d) and metal dispersion (D) of free,
stabilized and supported NPs.
Sample
dTEM (nm)
D (%)
[Rh(μ-Cl)(COD)]2 + 2KOH + 2MeOH → [Rh(μ-OMe)(COD)]2 + 2KCl +
2H2O (eq. 2)
Rh
Rh/Si
4.8
9.1
-
10
Synthesis of metal NPs supported
Rh-0.2L
Rh-0.2L/Si
1.5
1.6
-
58
The precursor, [Rh(μ-OMe)(COD)]2, was dissolved in 80 mL of THF, in
the presence of certain amount of (S,S)-DIPAMP ligand (L). The Rh/L ratio
varied from 0.2 to 1.0. The metal was reduced at 25 °C and 3 bar H2 under
stirring for 20 h.
Rh-0.4L
Rh-0.4L/Si
1.5
1.6
58
Appropriate amount of rhodium nanoparticles was added onto dried SiO2
obtaining 1wt% of Rh NPs on SiO2. THF was added at the mixture, it was
stirred overnight at 298 K, and then it was dried under vacuum for 3 h. Finally,
chirally modified catalyst was washed overnight with pentane (3 x 25 mL)
under vacuum at 40 °C.
Rh-0.7L
Rh-0.7L/Si
1.5
1.6
-
58
Rh-1.0L
Rh-1.0L/Si
1.5
1.7
-
54
Rhodium nanoparticles and 1wt% supported rhodium nanoparticles
samples were labeled as Rh-xL and Rh-xL/Si, respectively, were L represents
(S,S)-DIPAMP and x represents molar ratio of rhodium to ligand (Rh/L) ratio.
Catalysts characterization
Metal particle size (diameter) was determined by transmission electron
microscopy (TEM) and electron diffraction using JEOL JEM-1200 model
EXII. Metal dispersion on SiO2 was calculated from the relationship between
surface and total atoms. Additionally, mean particle size (cubic model) was also
estimated by TEM.
Nitrogen adsorption-desorption isotherms at 77 K were obtained in a
Micromeritics ASAP 2010 (CHEMI). Brunauer, Emmett and Teller (B.E.T)
and Barrett, Joyner and Halenda (B.J.H) models allowed to obtain specific
surface area, pore diameter and pore volume of all catalysts tested in this study.
XRD analyzes were performed using Rigatu New X-Ray “Geigerflex” D/
max-IIC (40 Kv, 2 mA) diffractometer in the 2θ range of 10 º to 90 º (λ=1.54056
Aº) at 1 º/min. XRD allows to identify the phases present in the catalysts.
TG analyses were conducted by TGA/SDTA 851e Mettler Toledo
Thermogravimetric Analyser on 100 mL/min Helium from 30 ºC to 800 ºC at
10 ºC/min. TG technique allows to relate the mass loss versus temperature and
possible interactions between metal and ligand.
Enantioselective hydrogenations reactions
Hydrogenation reactions were performed in a stainless steel semibatch
reactor coated with Teflon. Typically, 50 mL of solvent was used in all reactions
at 40 bar of pressure, room temperature, stirring speed of 800 rpm, and molar
ratio [substrate/metal] of 100. The solvent used for HD, EP and AP substrates
was cyclohexane and toluene for KP.
The experimental conditions used in this study were carefully selected to
avoid mass transfer limitations.
Analyses of reagents and products concentrations were determined using
a SHIMADZU GC-MS, model QP5050, equipped with a chiral column Beta
DEX 225 (Supelco) of 30 m long and 0.25 mm of diameter. Carrier gas used
was helium (99.995% of purity). Optical yields expressed as ee values, were
calculated with the following equation:
ee (%)= ([R]-[S])/([R]+[S])x100 (eq.3)
ee indicates the highest enantioselectivity value reached at the end of
selectemdaxreaction, when reactant conversion was completed.
RESULTS AND DISCUSSION
Catalysts characterization
Stabilized Rh nanoparticles showed smaller metal diameters than non-
stabilized Rh NPs for both free and supported NPs. Accordingly, stabilized
rhodium NPs exhibited high dispersion (58%) having average metal diameter
lower than 2 nm (see table 1). Conversely, non-stabilized Rh NPs displays
an average metal diameter as high as 9.1 nm showing metal dispersion of
10%. Additionally, results showed in table 1 revealed that stabilized free
and stabilized supported Rh nanoparticles posses similar metal particle size.
Figure 2 shows particle size distribution and TEM micrographs and of Rh
Figure 2. Size distribution histograms and TEM micrographs and of
stabilized and non-stabilized Rh catalysts.
2126

J. Chil. Chem. Soc., 58, Nº 4 (2013)
Specific surface area and pore volume determined from N adsorption-
desorption isotherms are displayed in Table 2. Supported samples,2in agreement
to the classification Brunauer, Deming, Deming and Teller (B.D.D.T), showed
type IV isotherms with a hysteresis loop. The isotherms are characteristic of
mesoporous solids mainly with pores cylindrical geometry. Specific surface
area values ranged from 136 to 76 (m2 g-1) for non-stabilized Rh and stabilized
catalysts, respectively indicating that ligand partially blochs the propus
structure of the support. The average pore diameter decreased from 31 to 18
nm as stabilized nanoparticles were deposited onto the pores of the support.
The molecular diameters of prochiral substrates are considerably smaller than
the pore diameter of the material. Therefore, it allows an appropriate diffusion
of the reactants and products from to the active sites.
Table 2 also compiles results obtained from TG analyses. All supported
catalysts show thermograms indicating that desorption of physisorbed water
is completed at 150°C and is followed by a broad region of weight loss, due
to dehydroxylation process. In thermograms the maximum loss of mass is
above to 400 °C until 550 °C. It can be seen an important increase of % weight
loss according with the amount of (S,S)-DIPAMP added in the NPs synthesis,
indicative of the chiral ligand is on catalysts surface. Decomposition around
500 °C is indicating that there is likely a chemical interaction between (S,S)-
DIPAMP and Rh/SiO2, as shown previous reports36.
Figure 3. Enantioselective hydrogenation of EP a) Reaction scheme,
b) conversion of EP on time with Rh-xL/Si catalysts and c) evolution of the
hydrogenation of EP on time using Rh-0.4L/Si. Reaction conditions: 0.02
mol L-1, at 40 bar of H2, 298 K and cyclohexane as solvent using 100 mg of
catalysts.
Table 2. Surface area, pore volume and mass loss of stabilized and non-
stabilized Rh catalysts.
The formation of 4-(R)-hydroxy-3-hexanone from HD achieved values
up to 54%. Maximum conversion was 94% at 300 min (Table 3, Fig. 4).
Although, similar behavior was expected for the reaction of AP, an aromatic
ketone, low conversion was observed due probably to an increased interaction
of the aromatic ring with the surface of the catalysts. However, further studies
are needed to draw a conclusion. This work shows promising results of
Catalyst
SB.E.T, m2 g-1
V pore, cm3 g-1
% wt lossa
Rh/Si
136
84
80
76
81
31
19
18
18
19
7.0
7.8
8.4
8.7
8.9
Rh-0.2L/Si
Rh-0.4L/Si
Rh-0.7L/Si
Rh-1.0L/Si
enantioselectivity in very scarcely studied substrates to date14,15
.
a % wt loss from 350 °C up to 600 °C.
No visible diffraction lines attributable to rhodium crystalline phase of
Rh-(x)L/Si catalysts appeared in XRD patterns, due to Rh has small particle
diameter and the metal loading in these catalysts were was 1% wt of rhodium.
On the contrary, non-stabilized Rh catalyst diffraction peaks, which had higher
average particle diameter, showed up 2θ = 41.0º and 47.3º representing (111)
and (200) planes of rhodium phase37. The most intense peak at 41.0 º was
corroborated by electron diffraction analysis showing Rh (111). As mentioned
elsewhere, XRD and electron diffraction analysis allow to verify crystalline
components on solid catalysts. Finally, electronic state of Rh on the surface
of each catalyst, after exposure to H2 at 30 ºC for 1 h, was analyzed by XPS
showing that rhodium-phase was mainly reduced. Previous work confirmed
that rhodium 3d5/2 appears mainly reduced at 307.3 eV binding energy14,15
.
Enantioselective hydrogenation reactions
The main objective of this study was to investigate catalytic activity and
selectivity in enantioselective hydrogenation reactions of supported rhodium
NPs stabilized by (S,S)-DIPAMP. Additionally, the nature of the substrate and
(S,S)-DIPAMP loading on supported rhodium NPs were also studied.
Typically, asymmetric hydrogenation of EP (Fig. 3a) is used as test reaction
in order to evaluate both activity and enantioselectivity of new catalysts16.
Consequently, Rh-xL/SiO2 catalysts were tested on the enantioselective
hydrogenation of EP, showed in Figure 3b, exhibiting good performance in the
transformation of EP.
According to previous works, as expected, the addition of a phosphorous
ligand such as (S,S)-DIPAMP allows to obtain the preferential formation of
the (R) with respect to (S) isomer15. In Figure 3c is shown the preferential
formation of (R)-ethyl lactate using Rh-0.4L/Si catalyst.
Figure 4. Enantioselective hydrogenation of HD, under following reaction
conditions: 0.02 mol L-1, 100 mg of Rh-xL/Si catalysts in cyclohexane at 40 bar
of H2 and 298 K. a) Reaction scheme, b) conversion on time.
The activity of Rh-xL/Si catalysts in the enantioselective hydrogenation of
KP is showed in Figure 5. All catalysts achieved complete conversion of KP
excepting Rh-0.4L/Si. Among all reactants tested, KP was quickly converted
at low reaction time attributed to high reactivity of these ketones. Furthermore,
keto group reactivity increases with the presence of the ester carbonyl group
in α position38.
In contrast to high conversion of KP, low ee values were accomplished as
shown in Table 3. This low enantioselectivity is probably because KP preferred
unmodified metal sites. The induction time observed on Rh-0.4L/Si catalyst
may be due to formation of dimers of KP. These side reactions may be limiting
enantiodifferentiation.
Contamination of catalyst surfaces can not be argued as a reason of
the induction time observed in this system, because it is well known that
clean surfaces are favored when organometallic precursors were used in the
preparation of heterogeneous catalysts29.
2127

J. Chil. Chem. Soc., 58, Nº 4 (2013)
Table 3. Conversion, enantioselectivity values and pseudo first-order rate constants of hydrogenation reactions of HD, EP, AP and KP. Conditions: 0.02 mol
L-1 of substrate and 100 mg of Rh-xL/Si catalysts in cyclohexane at 298 K and 40 bar of H2.
a% Conversion at 300 min of reaction.b Pseudo first-order rate constants was calculated up to 60 min. c% ee max referred to maximum value
of (R)-enantiomer.
2128

J. Chil. Chem. Soc., 58, Nº 4 (2013)
CONCLUSIONS
Chiral NPs can be synthesized under mild conditions using (S,S)-DIPAMP
as metal particle stabilizer. Stabilized supported Rh nanoparticles show metal
average smaller than 2.5 nm, with 58% of dispersion showing that aglomeration
of NPs can be controlled by this preparation method. Consequently, it was
shown that asymmetric catalysts tested for this study showed both high activity
and enantiomeric resolution in the evaluated reactions. Rh-0.2L/Si catalyst was
the most active catalyst for HD and AP enantioselective reactions, whereas for
the hydrogenation of KP was the Rh-0.7L/Si catalyst. Ethyl pyruvate showed
lower activity and selectivity levels with these catalysts. In the hydrogenation of
HD and AP, 54% and 46% of enantiomeric excess were obtained, respectively.
It was also found that ketones hydrogenation led to higher ee than α-keto esters
hydrogenations reactions. This paper shows that the activity and selectivity of
catalysts are directly related to the size and nature of the metal nanoparticles.
Non stabilized catalysts generated wide distribution of metal sizes on solids
and makes impossible the repeatability in hydrogenation reactions, obtaining
racemic mixtures of products.
ACKNOWLEDGEMENTS
This work was supported by the FONDECYT INICIACION project Nº
11121631.
REFERENCES
1. A. Roucoux, J. Schulz, H. Patin, Chem. Rev. 102, 3757, (2002).
2. H. Bönnemann, G. A. Braun, J. Chem. Eur. 3, 1200, (1997).
3. H. Bönnemann, G. A. Braun, Angew. Chem. Int. Ed. 35, 1992, (1996).
4. B. Chaudret, C. R. Physique. 6, 117, (2005).
Figure 5. Enantioselective hydrogenation of KP. a) Reaction scheme, b)
conversion on time under reaction conditions: 0.02 mol L-1, 100 mg of Rh-xL/
Si catalysts, 40 bar of H2 and 298 K in cyclohexane as solvent.
5. H. Bönnemann, R. M. Richards, Eur. J. Inorg. Chem. 10, 2455, (2001).
6. P. Barbaro, V. Dal Santo, F. Liguoric, Dalton Trans. 39, 8391, (2010).
7. D. Han, X. Li, H. Zhang, Z. Liu, J. Li, C. Li, J. Catal. 243, 318, (2006).
8. D. Han, X. Li b, H. Zhang, Z. Liu, G. Hu, Can Li, J. Mol. Cat A: Chem.
283, 15, (2008).
9. W. Xiong, H. Ma, Y. Hong, H. Chena, X. Lia, Tetrahedron Asym. 16, 1449,
(2005).
10. M. Jacinto, P. Kiyohara, S. Masunaga, R. Jardim, L. Rossi, Appl. Catal. A:
General. 338, 52, (2008).
Evolution of the enantioselective conversion of AP up to 300 minutes is
shown in Figure 6, and maximum enantioselectivity and maximum conversion
values are compiled in Table 3. It was found that Rh 0.2-L/Si achieved
maximum values of conversion (83%) among all catalysts tested in this system,
but lowest enantioselectivity value (46%). In contrast, Rh 0.4-L/Si achieved
highest value of enantioselectivity in this system (46%), but lowest value of
conversion (36%).
11. R. Somanathan, N. Cortez, M. Parra-Hake, D. Chávez, G. Aguirre. Mini-
Rev. Org. Chem, 313, 5, (2008).
12. S. Nath, S. Jana, M. Pradhan, T. Pal, J. Colloid Interface Sci, 341, 333
(2010).
13. A. Roucoux, Top. Organomet. Chem. 16, 261, (2005).
14. D. Ruiz, C. Mella, J. L. García Fierro, P. Reyes, J. Chil. Chem. Soc. 57,
1199, (2012).
15. D. Ruiz, M. Oportus, C. Godard, C. Claver, J.L García Fierro, P. Reyes,
Curr. Org. Chem. 16, 2754, (2012).
16. Y. Orito, S. Imai, S. Niwa, J. Chem. Soc. Jpn. 92, 1118, (1979).
17. P. Subramanian, S. Chatterjee, M. Bhatia, J. Chem.Technol. Biotechnol.
39, 215, (1987).
18. D. Gala, D. DiBenedetto, J. Clark, B. Murphy, D. Schumacher, Tetrahedron
Lett. 37, 611, (1996).
19. T. Marzialetti, J.L.G. Fierro, P. Reyes, J. Chil. Chem. Soc. 50, 391, (2005).
20. D. Ruiz, J.L.G. Fierro, P. Reyes. J. Braz. Chem. Soc. 21, 262, (2010).
21. A. Gual, C. Godard, K. Philippot, B. Chaudret, A. Denicourt-Nowicki, A.
Roucoux, S. Castillón, C. Claver, Chem. Sus. Chem. 2, 769, (2009).
22. T. Marzialetti , M .Oportus, D. Ruiz, J. L. García Fierro, P. Reyes, Catal.
Today. 133, 711, (2008).
23. A. Gual, M. R. Axet, K. Philippot, B. Chaudret, A. Denicourt-Nowicki, A.
Roucoux, S. Castillón, C. Claver, Chem. Commun. 2759, (2008).
24. S. Castillon, C. Claver, Y. Diaz, Chem. Soc. Rev. 34, 702, (2005).
25. M. Studer, H. U. Blaser, C. Exner, Adv. Synth. Catal. 345, 45, (2003).
26. J. Dupont, G. S. Fonseca, A. P. Umpierre, P. F. P. Fichtner, S. R. Teixeira,
J. Am. Chem. Soc. 124, 4228, (2002).
27. D. Ruiz, P. Reyes, J. Chil. Chem. Soc. 53, 1740, (2008).
28. P. Ellaiah, K. Krishna, Indian Drugs. 24, 192, (1987).
29. A. Roucoux, M. Devocelle, J. Carpentier, F. Agbossou, A. Mortreoux,
Synlett. 4, 358, (1995).
Figure 6. APhydrogenation: a) reaction scheme, b) evolution of conversion
on time. Reaction conditions: 0.02 mol L-1 of AP, 100 mg of Rh-xL/Si catalysts,
40 bar of H2 and 298 K in cyclohexane as solvent.
Finally, stability and reproducibility of this preparation method were
also considered in this study. Accordingly, preliminary studies using Rh/SiO
catalysts indicated that conversion values of EP can be keep for at least 3 cycles2.
Additionally, previous results also suggested no leaching of Rh during reaction.
30. T. Morimoto, H. Takahashi, K. Achiwa, Chem. Pharm. Bull. 42, 481,
(1994).
2129

J. Chil. Chem. Soc., 58, Nº 4 (2013)
31. M. Heitbaum, F. Glorius, I. Escher, Angew. Chem. Int. Ed.45, 4732, (2006).
32. R. Schmid, Chimia. 50, 110, (1996).
36. H. J. Zhu, Y. J. Ding, L. Yan, J. M. Xiong, Y. Lu, L. W. Lin, Catal. Today,
93, 389, (2004).
33. H. Brunner, A. Apfelbacher, M. Zabel, J. Inorg. Chem. 4, 917, (2001).
34. T. Sturm, W. Weissensteiner, F. Spindler, K. Mereiter, A. Lopez-Agenjo,
B. Manzano, F. Jalon, Organometallics, 21, 1766, (2002).
35. J. Sonnenberg, N. Coombs, P. Dube, R. Morris, J. Am. Chem. Soc, 134,
5893, (2012).
37. J. Haglund, A. Guillermet, G. Grimvall, M. Korling, Phys. Rev. B, 48,
11685, (1993).
38. X. B. Zuo, H. F. Liu, D. W. Guo, X. Z. Yang, Tetrahedron. 55, 7787,
(1999).
2130