Chemoselective Transfer Hydrogenation of Aldehydes and Ketones with a Heterogeneous Iridium Catalyst in Water

Article abstract of DOI:10.1007/s10562-014-1473-4

Ir nanocatalyst Ir@CN was prepared by pyrolysis of the IrCl₃ complex with 1,10-phenanthroline in the activated carbon. The iridium nanocatalyst Ir@CN was highly selective for the transfer hydrogenation of aldehydes and ketones including benzaldehyde derivatives, and the hydrogenative alkylation of C=O bonds was suppressed effectively. The iridium nanocatalyst Ir@CN is a heterogeneous catalyst and can be reused several times for the transfer hydrogenation of aldehydes and ketones.

Full text of DOI:10.1007/s10562-014-1473-4

Catal Lett
DOI 10.1007/s10562-014-1473-4
Chemoselective Transfer Hydrogenation of Aldehydes and
Ketones with a Heterogeneous Iridium Catalyst in Water
Zhi Wang
Rizhi Chen
Jun Huang
•
Lei Huang
•
•
Longfei Geng
Yong Wang
•
Weihong Xing
•
•
Received: 17 September 2014 / Accepted: 28 December 2014
Ó Springer Science+Business Media New York 2015
Abstract Ir nanocatalyst Ir@CN was prepared by pyro-
lysis of the IrCl complex with 1,10-phenanthroline in the
Keywords Ir nanocatalyst Á Transfer hydrogenation Á
Heterogeneous catalysts Á Aldehydes Á Ketones
3
activated carbon. The iridium nanocatalyst Ir@CN was
highly selective for the transfer hydrogenation of aldehydes
and ketones including benzaldehyde derivatives, and the
hydrogenative alkylation of C=O bonds was suppressed
effectively. The iridium nanocatalyst Ir@CN is a hetero-
geneous catalyst and can be reused several times for the
transfer hydrogenation of aldehydes and ketones.
1 Introduction
The reduction of carbonyl compounds to the corre-
sponding alcohols is an important chemical transforma-
tion in both academic research and industry application.
Historically, boron and aluminum hydride agents and
their derivatives were used as reductives for the reduction
of carbonyl compounds, and the method is still a reliable
route for the reduction of carbonyl compounds today [1–
5]. Transition metal catalyzed hydrogenation of carbonyl
compounds was investigated widely due to the advantages
of mild reaction conditions and high atom efficiency [6,
Graphical Abstract Ir nanocatalyst Ir@CN was prepared
and the Ir@CN was found to be highly selective for the
transfer hydrogenation of ketones and aldehydes including
benzaldehyde derivatives in water. The iridium nanocata-
lyst Ir@CN is a heterogeneous catalyst and can be reused
several times.
7
]. However, the hydrogenation of acetophenone, benz-
aldehyde and the derivatives is highly problematic since
the hydrogenative alkylation (by reaction) of carbonyl
group (benzoyl group) to methylene group is ready to be
occurred, and the corresponding alcohols were often
obtained in low yields [8, 9]. In order to overcome the
problem, homogeneous catalysts have been investigated
extensively and some reliable catalyst systems were
developed for the hydrogenation of aldehydes and ketones
[
10–14]. But the efficient heterogeneous catalysts were
few and the selectivity was always bad for the hydroge-
nation of aldehydes and ketones, especially for the
hydrogenation of acetophenone, benzaldehyde and the
derivatives [15–18]. Transition metal catalytic transfer
hydrogenation is an important and practical way for the
reduction of carbonyl compounds [19–25], as the hydro-
gen donors are easy to handle (without flammable and
explosive hydrogen gas and pressure vessels) and the mild
reaction conditions are used [26, 27].
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-014-1473-4) contains supplementary
material, which is available to authorized users.
JZ .. HW u aa nn gg Á(&L. H) uang Á L. Geng Á R. Chen Á W. Xing Á Y. Wang Á
State Key Laboratory of Materials-Oriented Chemical
Engineering. College of Chemistry and Chemical Engineering,
Nanjing Tech University, Nanjing 210009, China
e-mail: junhuang@njtech.edu.cn
123

Z. Wang et al.
Table 1 The reduction of 4-methyl benzaldehyde with different
catalysts
R1
R1
R2
O
OH
0.5% mol cat.
R2
O
OH
A
B
Scheme 1 Ir catalyzed the transfer hydrogenation of the carbonyl
compounds
Entry
Catalyst
Conv (%)
Yield A (%)
Yield B (%)
a
1
Pd/C
100
19
3
40
18
3
60
1
b
2 Experimental Section
2
Pd/C
a
3
Ir/C
0
b
2.1 The Preparation of Catalysts
4
Ir/C
47
4
43
4
4
a
5
Ir@CN
Ir@CN
0
b
IrCl Á3H O (0.034 g) was dissolved in ethanol (30 mL)
3
2
6
99
99
0
with stirring, then 1,10-phenanthroline monohydrate
Reaction conditions: 4-methyl benzaldehyde, 1 mmol, 0.5 mol %
catalyst (Ir or Pd), water, 3.5 mL. The conversion and yield were
determined by GC analysis (C16H34 used as internal standard)
(
0.062 g) was added into the solution at room temperature.
After stirring for another 1 h, activated carbon (0.93 g) was
added into the solution and the mixture was stirring for
10 h at 60 °C. After the mixture cooled to room tempera-
ture, the ethanol was removed by the rotary evaporation
under vacuum. The black solid was dried in a drying oven
at 60 °C under vacuum for 12 h, and then the solid was
transferred into a quartz boat and placed in the tube furnace
Bold Values indicate optimized (best) catalyst systems
a
H
2
balloon as reductant, 100 °C, 10 h
b
HCOOH, 3.5 mmol and NaOH, 2.0 mmol used; 100 °C, 18 h; Pd/C
and Ir/C prepared by impregnation methods
Since the first report of the transfer hydrogenation of the
carbonyl compounds in 1925 (Meerwein–Ponndorf–Verley
reaction) [28], various catalyst systems have been developed
for the reduction of carbonyl compounds. Some ruthenium
under N . The tube furnace was heated to 800 °C at the rate
2
of 10 °C per minute, and kept at 800 °C for 2 h under N2.
After the tube furnace cooled to room temperature, the
catalyst Ir@CN (containing Ir 2.01 wt%, detected by ICP)
was obtained as black powders.
[
[
29], iridium [30], rhodium [31] and palladium complexes
32] were reported for the transfer hydrogenation of carbonyl
compounds, but these systems were homogeneous and dif-
ficult to be recycled. Besides, some heterogeneous nano-
catalysts (nickel [33, 34], platinum nanoparticles [35] ) were
developed for the transfer hydrogenation of the carbonyl
compounds, but organic solvents were needed for the
transformation, and the selectivity was not good enough [36–
2.2 Typical Procedures for Transfer Hydrogenation
of Carbonyl Compounds
The transfer hydrogenation reactions were carried out
under argon atmosphere using standard Schlenk technique
unless otherwise stated. Benzyl aldehyde (1 mmol), formic
acid (3.5 eqiv.), and water (3.5 mL) were injected into a
sealed tube with the catalyst (0.048 g Ir@CN) and sodium
hydroxide (2 eqiv.) under Ar. Then the mixture was stirred
under 100 °C (with an oil bath) for the given time. After
cooled, the reaction mixture was diluted with 3 9 5 mL of
ether, and then the catalyst Ir@CN was filtered. The
conversions and yields were determined by GC using
n-hexadecane as an internal standard.
3
8]. Thus, the development of highly efficient and hetero-
geneous catalysts for the transfer hydrogenation of alde-
hydes and ketones (especially acetophenone, benzaldehyde
and the derivatives) are highly desirable as benzyl alcohols
are important intermediates for the synthesis of fragrances.
Recently, Fe and Co complexes with N contained
ligands were pyrolysed as heterogeneous catalysts for the
hydrogenation of nitro aromatics with high activity and
high selectivity [39, 40]. The 1,10-phenanthroline can be
linked with the activated carbon to form stable N-doped
carbon materials, which were used as good catalyst sup-
ports. Here, iridium nanoparticles were supported on
N-doped carbon materials as heterogeneous catalyst
Ir@CN, which was highly efficient and highly selective for
the transfer hydrogenation of carbonyl compounds to the
corresponding alcohols. Various carbonyl compounds
3 Results and Discussion
3.1 Catalyst Characterization
The Ir@CN catalyst was characterized by N adsorption,
2
(
aldehydes and ketones including acetophenone, benzal-
TEM, TGA and XPS. The N adsorption–desorption iso-
2
dehyde and the derivatives) were applicable for the transfer
hydrogenation, and the corresponding alcohols were
obtained in good to excellent yields (Scheme 1).
therms of AC and Ir@CN were shown in Fig. 1. The iso-
therm of the Ir@CN catalyst was typical IV curve (Type
H4) with nitrogen uptake under the relative pressure of
1
23

Chemoselective Transfer Hydrogenation
Fig. 3 The TG analysis of the precursor of Ir@CN
Fig. 1 N2 adsorption–desorption isotherms of the AC and Ir@CN
0
.5–1.0, which was always associated with narrow slit-like
pores. The BET surface areas of the AC and Ir@CN cat-
2
alyst were 1,706.7 and 1,456.2 m /g respectively. The pore
volume of the AC and Ir@CN catalyst were 1.15 and
3
.85 cm /g respectively, which meaned that some CN
0
material and Ir were filled into the pores of the AC. The
high resolution TEM (HRTEM) images in Fig. 2 gave
more details of Ir@CN catalyst and the recovered Ir@CN
after 3 reaction cycles. The Ir nanoparticles were highly
dispersed on the N hybrid carbon material, and the average
particle size of Ir was about 2–4 nm (Fig. 2a). Moreover,
the Ir nanoparticles in Ir@CN were quite stable, and the
particle size of Ir did not change evidently after three times
of the reaction (Fig. 2b). Since the catalyst Ir@CN was
prepared through high temperature (800 °C), the Ir nano-
particles were kept at about 2–4 nm, which indicated that
the Ir@CN was highly thermal stable, and the 1,10-phe-
nanthroline structure was highly beneficial for the stability
of the nanocatalyst Ir@CN. The TG curve of the precursor
of Ir@CN was presented in Fig. 3. Only very small slight
weight loss was observed at temperatures less than 550 °C
due to the desorption of moisture and constitutional water.
Fig. 4 Ir4f XPS spectra of 2 % Ir@CN catalyst
About 8 % weight loss was observed between 550–800 °C,
which meaned the stable N hybrid C material (CN) was
formed [39]. The XPS Ir4f and N1s spectra of the Ir@CN
catalyst are shown in Figs. 4 and 5 respectively. According
to the binding energies of Ir4f7/2 at 61 eV and Ir4f5/2 at
Fig. 2 TEM micrographs of
a fresh Ir@CN; b recovered
Ir@CN after 3 reaction cycles
123

Z. Wang et al.
6
4.2 eV, iridium species in the catalyst Ir@CN was
reduced to metallic state Ir (0) after being treated at 800 °C
41, 42]. Moreover, the N1s binding energies of pyridine-
transfer hydrogenation of 4-methyl benzaldehyde. But the
Ir nanoparticles in Ir/C can not be retained without phe-
nanthroline linked on the surface of the AC when the
catalyst heated to 800 °C, thus the catalyst Ir/C was not
active for the transformation. The optimization of the
reaction conditions was provided in the supplementary
material.
[
type nitrogens were at 399.0 and 400.8 eV, which indicated
that the phenanthroline structure was kept and coordinated
with the Ir nanoparticles [39].
3
.2 The Reduction of 4-Methyl Benzaldehyde
with Different Catalysts
3.3 The Transfer Hydrogenation of Carbonyl
Compounds with Ir@CN
The reduction of 4-methyl benzaldehyde was chosen as a
template reaction to test the Ir@CN catalyst. For compar-
ison, Pd/C, Ir/C and Ir@CN were used for the transfer
hydrogenation of 4-methyl benzaldehyde and hydrogena-
Using the optimized reaction conditions, the Ir@CN cata-
lyst was used for the transfer hydrogenation of carbonyl
compounds to the corresponding alcohols. Various alde-
hydes and ketones were used for the transfer hydrogenation
under the optimized conditions, the results are summarized
in Table 2. A range of aromatic aldehydes can be transfer
hydrogenated to the corresponding alcohols in good to
excellent yields (Table 2, entry 1–11). The transfer
hydrogenation of benzaldehyde gave benzyl alcohol in
quantitative yield (Table 2, entry 1). When the benzalde-
hydes substituted with halides (F and Cl) were used, no
dehalogenation was detected, and the corresponding benzyl
alcohols were obtained in high yields (Table 2, entry 2, 3, 5
and 6). The transfer hydrogenation of bromobenzaldehyde
afforded the corresponding benzyl alcohols in 90–95
yields, and small amount of benzyl alcohol generated by
the side reaction dehalogenation (Table 2, entry 4 and 7).
The transfer hydrogenation of benzaldehydes with meth-
oxyl and methyl groups gave the corresponding benzyl
alcohols in excellent yields (Table 2, entry 8–11). More-
over, 1-naphthaldehyde can be converted smoothly to
1-naphthalenemethanol in high yield (Table 2, entry 12).
Furthermore the Ir@CN catalyst was highly active and
selective for the transfer hydrogenation of heterocyclic
aldehydes, and furfural alcohol and 2-pyridylmethanol
were obtained in high yields respectively (Table 2, entry
tion of 4-methyl benzaldehyde with H (Table 1). When H2
2
was used as reductant (under 1 atm), Pd/C was highly
active for the hydrogenation of 4-methyl benzaldehyde.
4
4
-Methyl benzaldehyde was converted completely, but
-methylbenzyl alcohol was obtained only in 40 % yield,
and p-xylene (hydrogenative alkylation) was obtained in
0 % yield. (Table 1, entry 1). By contrast, Ir/C and
6
Ir@CN were not active for the hydrogenation 4-methyl
benzaldehyde with H , and the conversion of 4-methyl
2
benzaldehyde was low with both Ir/C and Ir@CN (Table 1,
entry 3, 5). Then, we tested the transfer hydrogenation of
4
-methyl benzaldehyde with HCOOH/NaOH as a reducing
agent using Pd/C, Ir/C and Ir@CN catalysts. Delightedly,
Ir@CN was not only highly active but also highly selective
for the transfer hydrogenation of 4-methyl benzaldehyde,
and 4-methylbenzyl alcohol was obtained in 99 % yield
(
Table 1, entry 6). But the Pd/C and Ir/C were not active
enough for the transfer hydrogenation of 4-methyl benz-
aldehyde, and 4-methylbenzyl alcohol was obtained in low
yield (Table 1. entry 2, 4). The Ir nanoparticles in Ir@CN
catalyst were stablized by the linked 1,10-phenanthroline
structure, and showed high activity and selectivity for the
13–14). Besides, aliphatic aldehydes were also applicable
for the transfer hydrogenation, and cyclohexanecarbox-
aldehyde, 1-pentanal, 1-hexanal, 1-octanal and phenyl
propyl aldehyde were converted to the corresponding
alcohols in good to excellent yields (Table 2, entry 15–19).
And then, unsaturated aldehydes 3-cyclohexene-1-carbox-
aldehyde and cinnamaldehyde were tested for the transfer
hydrogenation with Ir@CN catalyst, and 3-cyclohexene-1-
methanol and cinnamic alcohol were obtained in 90 and
65 % yields respectively (Table 2, entry 20, 21). In addi-
tion to aldehydes, ketones were also tested for the transfer
hydrogenation with Ir@CN catalysts. Cyclohexanone was
converted to cyclohexanol smoothly in high yield, but the
transfer hydrogenation of acetophenone gave correspond-
ing alcohol in moderate yield under harsher reaction
conditions.
Fig. 5 N1s XPS spectra of 2 % Ir@CN catalyst
1
23

Chemoselective Transfer Hydrogenation
Table 2 The transfer hydrogenation aldehydes and ketones to
alcohols
Table 2 continued
Entry
Substrate
Yield (%)
1
5
[99
O
1
1
6
7
O
[99
Entry
1
Substrate
Yield (%)
99
O
[99
1
1
8
9
O
75 (95)
O
O
O
[99
2
3
F
99
b
90
2
0
1
O
O
Cl
[99
c
65
2
d
22
O
93
O
4
Br
90
e
3
2
O
65 (91)
O
5
6
[99
[99
Reaction conditions: substrate, 1.0 mmol; water, 3.5 mL; tempera-
ture, 100 °C; reaction time, 18 h; HCOOH, 3.5 mmol; NaOH,
F
O
2
with 24 h. Conversion and yield were determined by GC analysis
.0 mmol; Ir@CN catalyst, 48 mg, Ir (0.5 %); yields in parentheses
Cl
(
16
C H34 used as internal standard)
O
a
By-product was 4-methylanisole
7
8
9
95
b
Yield of 3-cyclohexene-1-methanol, and the by-product was
cyclohexane methanol
Br
O
c
Yield of cinnamic alcohol, major by-product was phenyl propyl
a
80
alcohol
d
MeO
Ir@CN catalyst, 10 mg, Ir (0.1 %)
O
e
Ir@CN catalyst, 96 mg, Ir (1 %)
OMe
[99
[99
O
3
.4 Catalyst Reusability
1
0
Finally, the recyclability of the Ir@CN catalyst was tested,
and the results are listed in Table 3. The Ir@CN catalyst
can be used at least four times without obvious loss of
activity. The activity decreased slightly was due to the loss
of the Ir@CN catalyst during the recovery of the catalyst
O
1
1
1
2
[99
O
(filtration and drying of the Ir@CN). Furthermore, no Ir
88 (98)
was detected in the filtrate after filtration of the Ir@CN
catalyst (by ICP), which meaned no Ir leached into the
reaction solution, and the Ir@CN is a real heterogeneous
catalyst for the transfer hydrogenation of aldehydes and
ketones. With 1,10-phenanthroline structure tethered on the
surface of the AC, Ir nanoparticles were homogeneously
dispersed on the nitrogen-carbon surface in the Ir@CN
catalyst, which afforded excellent activity and stability of
the Ir@CN catalyst.
O
1
1
3
4
O
99
95
O
N
O
123

Z. Wang et al.
9
. Ley SV, Stewart-Liddon AJ, Pears D, Perni RH, Treacher K
(
Table 3 Recycling of the catalyst
2006) Beilstein J Org Chem 2:15
0. Jimenez-Sanchidrian C, Ruiz JR (2014) Appl Catal
469:367–372
1. Battilocchio C, Hawkins JM, Ley SV (2013) Org Lett
5:2278–2281
2. Azua A, Mata JA, Peris E, Lamaty F, Martinez J, Colacino E
2012) Organometallics 31:3911–3919
3. Barge A, Tagliapietra S, Tei L, Cintas P, Cravotto G (2008) Curr
Org Chem 12:1588–1612
4. Deshmukh R R, Rajagopal R, Srinivasan K (2001) Chem
Commun 1544–1545
0.5 mol% Ir@CN
1
1
1
1
1
A
HCOOH
O
OH
1
Recycled No.
Yield (%)
(
1
2
3
4
97
96
92
90
1
1
1
5. Noyori R, Hashiguchi S (1997) Acc Chem Res 30:97–102
6. Palmer MJ, Wills M (1999) Tetrahedron 10:2045–2061
7. Everaere K, Mortreux A, Carpentier JF (2003) Adv Synth Catal
Reaction conditions: 4-methyl benzaldehyde, 1 mmol; water, 3.5 mL;
temperature, 100 °C; time, 18 h; HCOOH, 3.5 mmol; NaOH,
2.0 mmol; Ir@CN catalyst, 48 mg, Ir (0.5 %); yield determined by
GC analysis (C16H34 used as internal standard)
3
45:67–77
8. Wei Y, Xue D, Lei Q, Wang C, Xiao J (2013) Green Chem
5:629–634
1
1
1
9. Ikariya T, Murata K, Noyori R (2006) Org Biomol Chem
4:393–406
4
Conclusions
2
2
0. Gladiali S, Alberico E (2006) Chem Soc Rev 35:226–236
1. Samec JS, Backvall J-E, Andersson PG, Brandt P (2006) Chem
Soc Rev 35:237–248
2. Clapham SE, Hadzovic A, Morris RH (2004) Coord Chem Rev
248:2201–2237
3. Selvam P, Sonavane S, Mohapatra S, Jayaram R (2004) Adv
Synth Catal 346:542–544
4. Mizugaki T, Kanayama Y, Ebitani K, Kaneda K (1998) J Org
Chem 63:2378–2381
In summary, Ir nanocatalyst Ir@CN was developed and the
Ir@CN catalyst was highly selective for the transfer
hydrogenation of carbonyl compounds into the corre-
sponding alcohols in water. The Ir@CN catalyst was
applicable widely for the transfer hydrogenation of alde-
hydes and ketones including benzaldehyde derivatives, and
the alcohols were obtained in good to excellent yields as
the hydrogenative alkylation of C=O bonds was suppressed
effectively. Moreover, the iridium nanocatalyst Ir@CN is
highly stable, heterogeneous and reusable for the transfer
hydrogenation of aldehydes and ketones.
2
2
2
25. Chen B, Dingerdissen U, Krauter J, Lansink Rotgerink H, Mobus
K, Ostgard D, Panster P, Riermeier T, Seebald S, Tacke T (2005)
Appl Catal A 280:17–46
2
2
6. Ikariya T, Blacker AJ (2007) Acc Chem Res 40:1300–1308
7. Kohen A (2007) In: Hynes JT, Klinman JP, Limbach HH,
Schowen RL (eds) Hydrogen transfer reactions.
2
2
8. Nishide K, Node M (2002) Chirality 14:759–767
9. Enthaler S, Jackstell R, Hagemann B, Junge K, Erre G, Beller M
Acknowledgments This work was supported by the National Nat-
ural Science of Foundation of China (Grant No. 21136005), the
National High Technology Research and Development Program of
China (No. 2012AA03A606) and the Project of Priority Academic
Program Development of Jiangsu Higher Education Institutions
(
2006) J Organomet Chem 691:4652–4659
0. Zhou Z, Ma Q, Zhang A, Wu L (2011) Appl Organomet Chem
5:856–861
3
3
3
3
2
1. Bogar K, Krumlinde P, Bacsik Z, Hedin N, Backvall JE (2011)
Eur J Org Chem 2011:4409–4414
2. Islam SM, Roy AS, Mondal P, Salam N (2012) Appl Organomet
Chem 26:625–634
3. Alonso F, Calvino JJ, Osante I, Yus M (2005) Chem Lett
(
PAPD, 38701001).
3
4:1262–1263
34. Alonso F, Calvino JJ, Osante I, Yus M (2006) J Exp Nanosci
:419–433
References
1
3
3
3
5. Alonso F, Riente P, Rodriguez-Reinoso F, Ruiz-Martinez J,
Sepulveda-Escribano A, Yus M (2008) J Catal 260:113–118
6. Fujii A, Hashiguchi S, Uematsu N, Ikariya T, Noyori R (1996) J
Am Chem Soc 118:2521–2522
7. Uematsu N, Fujii A, Hashiguchi S, Ikariya T, Noyori R (1996) J
Am Chem Soc 118:4916–4917
8. Clark JH, Tavener SJ (2007) Org Process Res Dev 11:149–155
9. Westerhaus FA, Jagadeesh RV, Wienhofer G, Pohl M-M, Radnik
J, Surkus A-E, Rabeah J, Junge K, Junge H, Nielsen M, Bruckner
A, Beller M (2013) Nat Chem 5:537–543
0. Jagadeesh RV, Surkus AE, Junge H, Pohl MM, Radnik J, Rabeah
J, Huan H, Schunemann V, Bruckner A, Beller M (2013) Science
1
2
. Chen X, Jia W, Guo R, Graham T W, Gullons M A, Abdur-
Rashid K (2009) Dalton Trans 1407–1410
. Doucet H, Ohkuma T, Murata K, Yokozawa T, Kozawa M,
Katayama E, England AF, Ikariya T, Noyori R (1998) Angew
Chem Int Ed 37:1703–1707
3
4
5
6
7
8
. Mikami K, Korenaga T, Terada M, Ohkuma T, Pham T, Noyori R
3
3
(
1999) Angew Chem Int Ed 38:495–497
. Ohkuma T, Koizumi M, Muniz K, Hilt G, Kabuto C, Noyori R
2002) J Am Chem Soc 124:6508–6509
(
. Ohkuma T, Ooka H, Hashiguchi S, Ikariya T, Noyori R (1995) J
Am Chem Soc 117:2675–2676
. Wu X, Liu J, Li X, Zanotti-Gerosa A, Hancock F, Vinci D, Ruan
J, Xiao J (2006) Angew Chem Int Ed Engl 45:6718–6722
. Zassinovich G, Mestroni G, Gladiali S (1992) Chem Rev
4
3
42:1073–1076
4
4
1. Ledesma BC, Valles VA, Rivoira LP, Martinez ML, Anunziata
OA, Beltramone AR (2014) Catal Lett 144:783–795
2. Rojas JV, Castano CH (2014) J Nanopart Res 16:2567
9
2:1051–1069
. Yu J -Q, Wu H -C, Ramarao C, Spencer J B, Ley S V (2003)
Chem Commun 678–679
1
23