Porous chitosan-MnO2 nanohybrid: A green and biodegradable heterogeneous catalyst for aerobic oxidation of alkylarenes and alcohols

Article abstract of DOI:10.1002/aoc.3412

A porous chitosan-manganese dioxide (PC-MnO₂) nanohybrid was synthesized using an in situ reduction method, in which potassium permanganate solution and nanoporous chitosan acted as precursor and reducing agent. The chemical and structural properties of PC-MnO₂ were characterized using scanning and transmission electron microscopies, X-ray diffraction, thermogravimetric analysis and Fourier transform infrared spectroscopy. Highly dispersed MnO₂ nanoparticles in a matrix of porous chitosan showed high catalytic activity for selective aerobic oxidation of alkylarenes and alcohols without using any bases or expensive oxidants. Short reaction time, ease of product separation by filtration and recyclability of the catalyst make it environmentally and economically favoured for the synthesis of versatile aldehydes and ketones.

Full text of DOI:10.1002/aoc.3412

Full paper
Received: 26 August 2015
Revised: 21 October 2015
Accepted: 29 October 2015
Published online in Wiley Online Library: 22 December 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3412
Porous chitosan–MnO2 nanohybrid: a green
and biodegradable heterogeneous catalyst for
aerobic oxidation of alkylarenes and alcohols
Ahmad Shaabani*, Mahmoud Borjian Boroujeni and Mohmmad Sadegh Laeini
A porous chitosan–manganese dioxide (PC–MnO2) nanohybrid was synthesized using an in situ reduction method, in which
potassium permanganate solution and nanoporous chitosan acted as precursor and reducing agent. The chemical and structural prop-
erties of PC–MnO2 were characterized using scanning and transmission electron microscopies, X-ray diffraction, thermogravimetric
analysis and Fourier transform infrared spectroscopy. Highly dispersed MnO2 nanoparticles in a matrix of porous chitosan showed
high catalytic activity for selective aerobic oxidation of alkylarenes and alcohols without using any bases or expensive oxidants. Short
reaction time, ease of product separation by filtration and recyclability of the catalyst make it environmentally and economically
favoured for the synthesis of versatile aldehydes and ketones. Copyright © 2015 John Wiley & Sons, Ltd.
Keywords: porous chitosan; MnO2; nanohybrid; aerobic oxidation; alkylarenes; alcohols
but can also reduce KMnO4 to MnO2. Since chitosan is a biopoly-
mer, precious metal or other metal oxides can be separated easily
Introduction
Oxidation reactions play an important role in organic chemistry
and they represent one of the challenging topics in chemistry.[1]
Valuable oxygen-containing intermediates such as alcohols,
ketones and aldehydes have become necessary as starting
materials for large-scale production in the pharmaceutical and
chemical industries.[2] During the last two decades, a large num-
ber of useful oxidation reactions using heterogeneous and
homogeneous catalysts have been introduced.[3] In recent years,
there has been a growing demand for the development of green,
inexpensive and environmentally benign aerobic catalytic systems
that can operate under moderate conditions with a high degree
of selectivity.[4,5]
by chemical decomposition or burning after deactivation of
catalyst.
In view of our main objectives of developing eco-friendly hetero-
geneous catalysts for organic transformations,[20–27] herein we
report the in situ synthesis of a biodegradable porous chitosan–
manganese dioxide (PC–MnO2) nanohybrid as a heterogeneous
catalyst. Its catalytic activities were investigated for the aerobic ox-
idation of alkylarenes and alcohols to the corresponding carbonyl
compounds in p-xylene in the presence of 5 mol% of PC–MnO2.
To the best of our knowledge, a chitosan–MnO2 nanohybrid has
not been used previously as a catalyst in aerobic oxidation
reactions.
MnO2 as an environmentally friendly oxidant of low cost and
with ease of handling and high activity has tremendous poten-
tial in a variety of organic transformations in simple reaction
procedures.[6,7] However, excess MnO2 (400–4000 wt% or 4- to
40-fold excess by weight) as an oxidant reagent is required for
achieving sufficient oxidation results.[8] To overcome this prob-
lem, MnO2 can be dispersed and immobilized onto various
organic and inorganic supports such as alumina,[9] ZrO2,[9]
TiO2,[10] silica,[11] aluminium silicate,[12] SBA-15,[13] graphene
oxide,[14] graphite[15] and cellulose to obtain heterogeneous
catalysts with required lower amounts of MnO2.[16] Nonetheless,
in some cases, oxidation only occurs using excess amounts of
MnO2/support.[12,15] In addition, to the best of our knowledge,
the separation of MnO2 from inorganic supports after deactiva-
tion of catalyst is usually difficult and reuse of MnO2 is not cost
effective.[17]
Experimental
Materials and methods
Chitosan (degree of deacetylation = 88%, molecular weight = 100
000–300 000 g molÀ1) was purchased from Sigma-Aldrich. Other
chemicals were purchased from Merck and used without further
purification. Powder X-ray diffraction (XRD) data were collected
with a STOE STADI P with scintillation detector and secondary
monochromator using Cu Kα radiation. Scanning electron
microscopy (SEM) images were obtained using
XL-30ESEM equipped with an EDAX microprobe. The morphol-
ogy of the catalyst was examined using transmission electron
a Philips
*
Correspondence to: Ahmad Shaabani, Faculty of Chemistry, Shahid Beheshti
University, GC, PO Box 19396-4716, Tehran, Iran.
E-mail: a-shaabani@sbu.ac.ir
Natural organic polymers such as chitosan are interesting mate-
rials for use as supports for catalytic applications due to low cost,
high surface area, biodegradability, biocompatibility and non-
toxicity.[18,19] In addition, amine and hydroxyl groups of chitosan
are not only able to chelate with metal ions and metal oxides
Faculty of Chemistry, Shahid Beheshti University, GC, PO Box 19396-4716, Tehran,
Iran
Appl. Organometal. Chem. 2016, 30, 154–159
Copyright © 2015 John Wiley & Sons, Ltd.

Porous chitosan–MnO2 nanohybrid: a green and biodegradable catalyst
microscopy (TEM; Zeiss-EM10C-80 KV, Germany). Fourier trans-
form infrared (FT-IR) spectra were recorded with a Bomem
MB-Series FT-IR spectrophotometer. Thermogravimetric analysis
(TGA) was conducted using an STA 1500 instrument at a heating
rate of 10 °C minÀ1 in air. Manganese determination was carried
out using flame atomic absorption spectroscopy (FAAS; Shimadzu
model AA-680) with a manganese hollow cathode lamp, using an
air–acetylene flame. Products were analysed using the internal
standard method with an Agilent 7890A gas chromatograph.
Preparation of PC–MnO2 nanohybrid
A PC membrane was constructed according to previous work.[28]
Firstly, chitosan (0.20 g) and PEG 6000 (0.20 g) were dissolved in
an aqueous acetic acid solution (20 ml, 2%) at room temperature.[27]
The solution was then spread uniformly on the surface of a glass
plate and dried at 50°C for 8 h. After drying, the membrane was im-
mersed in an aqueous sodium hydroxide solution (20 ml, 2% w/v)
for 1 h. The membrane was heated in water to remove the PEG
component at 80 °C for 8 h. PC was soaked in an aqueous
potassium permanganate solution (12 ml, 0.1M) for 24h. The
resulting dark-brown PC–MnO2 nanohybrid was separated and
washed with water and dried at 50 °C for 8 h. Finally, the
PC–MnO2 nanohybrid was ground to obtain a powder.
Scheme 1. Preparation of PC–MnO2 nanohybrid.
agent to produce MnO2 nanoparticles by in situ reduction of
potassium permanganate and (ii) as a bio-template that controls
the shape and size of MnO2 nanoparticles and prevents aggre-
gation and leaching of nanoparticles.
The FT-IR spectra of chitosan and catalyst are shown in
Fig. 1. A strong band appears around 500 cmÀ1 which is
characteristic for Mn–O. The band at 1728 cmÀ1 indicates
that hydroxyl groups of chitosan are oxidized to aldehyde
groups in the chitosan matrix. These results confirm the
oxidation of chitosan by potassium permanganate solution
and the formation of MnO2 nanoparticle in situ under neutral
conditions.
General procedure for oxidation of alkylarenes
Alkylarenes (1mmol) were added to a round-bottomed glass flask
fitted with a reflux condenser containing a mixture of PC–MnO2
nanohybrid (5mol%, 0.04g) in 5 ml of p-xylene. The mixture was
heated at 100°C with continuous bubbling of air with a flow rate
of 15 ml minÀ1. After completion of the reaction, the catalyst was
separated by filtration and crude product was used for GC
analysis.
Gram-Scale reaction
9H-xanthene (10 mmol, 1.82 g) was added to a round-bottomed
glass flask fitted with a reflux condenser containing a mixture of
PC–MnO2 nanohybrid (5mol%, 0.4 g) in 50 ml of p-xylene. The
mixture was heated at 100°C for 5 h with continuous bubbling of
air with a flow rate of 15 mlminÀ1. After completion of the reaction,
the mixture was cooled to room temperature and the catalyst
was separated by filtration and the solvent was evaporated.
9H-xanthen-9-one as a main product was isolated in 90% yield
(1.76g). Its melting point was 170–172 °C.
Figure 1. FT-IR spectra of (A) chitosan and (B) PC–MnO2 nanohybrid.
General procedure for oxidation of alcohols
An alcohol (1 mmol) was added to a round-bottomed glass flask
fitted with a reflux condenser containing a mixture of PC–MnO2
nanohybrid (5 mol%, 0.04 g) in 5 ml of p-xylene. The mixture
was heated at 80 °C with continuous bubbling of air with a flow
rate of 15 ml minÀ1. After completion of the reaction, the catalyst
was separated by filtration and crude product was used for GC
analysis.
Results and discussion
The PC–MnO2 nanohybrid was synthesized by soaking PC in
potassium permanganate solution (Scheme 1). In this synthetic
protocol, chitosan has two important roles: (i) as a reducing
Figure 2. TGA curves of (A) chitosan, (B), PC and (C) PC–MnO2 nanohybrid.
Appl. Organometal. Chem. 2016, 30, 154–159
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

A. Shaabani et al.
The TGA curves of chitosan, PC and PC–MnO2 nanohybrid were
obtained under air atmosphere (Fig. 2). For the PC–MnO2
nanohybrid, there are two steps of mass losses at temperatures
of 50–200 and 200–460 °C. In the first step, adsorbed water is
removed; in the second step, decomposition of PC occurs.
The XRD patterns of chitosan and PC–MnO2 nanohybrid are
shown in Fig. 3. An amorphous form of chitosan reveals a sharp
peak at 2θ = 20°. After synthesis of porous form of chitosan, the
crystalline structure of chitosan is changed and the intensity of
the peak at 2θ = 20° strongly decreases. No MnO2 peaks are
observed in the diffractogram of PC–MnO2 nanohybrid, mean-
ing that the MnO2 particles are not composed of single
crystallites.[29]
As shown in Figs. 4(A) and (B), the SEM images reveal the for-
mation of a nanoporous structure of chitosan. The chemical
composition of the PC–MnO2 nanohybrid was investigated using
energy dispersive spectroscopy (EDS). The EDS analysis clearly
illustrates the presence of manganese in the catalyst (Fig. 4(C)).
TEM images of the catalyst are shown in Fig. 5. The chitosan
exhibits a three-dimensional nanoporous structure with a pore
size of about 150 nm. The size and morphology of MnO2 nano-
particles are shown in Fig. 5. MnO2 nanoparticles are found to
be monodispersed and the average particle size is smaller than
10nm. According to FAAS analysis, the amount of MnO2 is
12wt%.
The catalytic activity of the synthesized PC–MnO2 nanohybrid
was investigated in the aerobic oxidation of alkylarenes. Aero-
bic oxidation of diphenylmethane was selected as a model
reaction, and the effects of solvent, temperature and amount
of catalyst on oxidation were studied. As indicated in Table 1,
maximum conversion is achieved using p-xylene at 100 °C.
Figure 3. XRD patterns of (A) chitosan and (B) PC–MnO2 nanohybrid.
Figure 4. (A, B) SEM images and (C) EDS analysis of PC–MnO2 nanohybrid.
Figure 5. TEM images of PC–MnO2 nanohybrid.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 154–159

Porous chitosan–MnO2 nanohybrid: a green and biodegradable catalyst
The results show that the desired conversion and reaction rate
are obtained using 5 mol% of the catalyst (Table 1, entries
7–11). The optimum conditions are determined to be: p-xylene
(10 ml) as solvent, 5 mol% (0.04 g) of catalyst in ambient air
at 100 °C.
To determine catalyst efficiency for aerobic oxidations, a
large variety of alkylarenes were subjected to the optimized
conditions. Aerobic oxidation of reactants with two benzylic
sites was carried out selectively at one position (Table 2,
entries 4 and 5). The PC–MnO2 nanohybrid catalysed the
oxidation of benzylic ether to the corresponding lactone
(Table 2, entry 8).
performed as a model reaction. The best conditions for aerobic
oxidation of phenylethyl alcohol are 5 mol% of catalyst in
p-xylene at 80 °C using ambient air as oxidant. The results are
summarized in Table 3.
As evident from Table 4, under optimum reaction conditions,
various primary and secondary aliphatic and aromatic alcohols are
converted to the corresponding aldehydes and ketones in high
yields at 0.5–3 h.
The results of our research were compared with those of previ-
ous reports of oxidation by MnO2 with respect to yields, solvents,
temperatures, amounts of MnO2 and reaction times. As evident
from Table 5 (entry 5), a reasonable yield is obtained in a short reac-
tion time and with a catalytic amount of PC–MnO2 nanohybrid. In
addition MnO2 is separated easily from chitosan after deactivation
of the catalyst by burning.
In order to further investigate the activity of the catalyst, the
scope of the aerobic oxidation was expanded to various aliphatic
and aromatic alcohols. The oxidation of phenylethyl alcohol was
Table 1. Effect of solvent, temperature and amount of catalyst on
oxidation of diphenylmethane catalysed by PC–MnO2 nanohybrida
Table 3. Effects of solvent, temperature, time and amount of catalyst
on oxidation of phenylethyl alcohol catalysed by PC–MnO2 nanohybrida
Entry
Solvent
Amount of
Time Temperature Yield
catalyst (mol%)
(h)
(°C)
(%)b
Entry
Solvent
Amount of
Time Temperature Yield
catalyst (mol%)
(h)
(°C)
(%)
1
Toluene
5
5
8
100
65
80
30
30
10
0
2
n-Hexane
Ethyl acetate
EtOH
16
12
14
20
7
1
Toluene
5
5
5
5
5
-
0.7
3
100
65
70
75
100
80
80
80
80
80
80
80
85
50
50
40
15
5
3
5
70
2
n-Hexane
Ethyl acetate
EtOH
4
5
70
3
3
5
H2O
5
100
100
100
100
100
100
100
100
4
2
6
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
—
1
0
5
H2O
8
7
7
50
60
80
85
95
45c
6
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
p-Xylene
8
8
2
7
7
1
2
3
4
5
5
4
60
70
80
85
95
50b
9
3
7
8
3
10
11
12
4
7
9
2
5
6
10
11
12
1
5
18
0.3
8
aReaction conditions: diphenylmethane (1 mmol), 5 ml of solvent, air.
bYield determined by GC analysis.
cActivated MnO2 used as a catalyst.
aReaction conditions: phenylethyl alcohol (1 mmol), solvent (5 ml), air.
bActivated MnO2 used as a catalyst.
Table 2. Aerobic oxidation of alkylarenes catalysed by PC–MnO2 nanohybrida
Entry
Alkylarene
Diphenylmethane
Product
Benzophenone
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
5
7
7
6
6
4
5
7
90
95
95
90
90
95
95
90
Ethylbenzene
Acetophenone
Propylbenzene
Propiophenone
1,2,3,4-Tetrahydronaphthalene
2,3-Dihydro-1H-indene
9H-fluorene
3,4-Dihydronaphthalen-1(2H)-one
2,3-Dihydro-1H-inden-1-one
9H-fluoren9-one
9H-xanthene
9H-xanthen-9-one
1,3-Dihydroisobenzofuran
Isobenzofuran-1(3H)-one
aReaction conditions: alcohol (1 mmol), PC–MnO2 nanohybrid (5 mol%, 0.04 g), p-xylene (5 ml), 100 °C, air.
bYield determined by GC analysis.
Appl. Organometal. Chem. 2016, 30, 154–159
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

A. Shaabani et al.
Table 4. Aerobic oxidation of alcohols catalysed by PC–MnO2 nanohybrida
Entry
Alcohol
Product
Acetophenone
Time (h)
Yield (%)b
1
1-Phenylethan-1-ol
Benzyl alcohol
1
90
90
95
100
90
95
95
75
90
90
85
90
90
90
80
80
70
75
85
85
2
Benzaldehyde
0.5
1
3
9H-fluoren-9-ol
9H-fluoren-9-one
Benzil
4
Benzoin
0.6
1
5
1-Phenylpropan-1-ol
Diphenylmethanol
2,3-Dihydro-1H-inden-1-ol
Cinnamyl alcohol
4-Fluorobenzyl alcohol
4-Bromobenyl alcohol
4-Cholorobenzyl alcohol
4-Nitrobenzyl alcohol
4-Methylbenzyl alcohol
4-Methoxybenzyl alcohol
3-Phenylpropan-1-ol
2-Phenylethan-1-ol
Octan-1-ol
Propiophenone
6
Benzophenone
0.6
2
7
2,3-Dihydro-1H-inden-1-one
Cinnamaldehyde
4-Fluorobenzylaldehyde
4-Bromobenzylaldehyde
4-Cholorobenzylaldehyde
4-Nitrobenzylaldehyde
4-Methylbenzylaldehyde
4-Methoxybenzylaldehyde
3-Phenylpropanal
2-Phenylacetaldehyde
Octanal
8
3
9
2
10
11
12
13
14
15
16
17
18
19
20
2
2
3
0.6
0.6
3
2.30
7
Cyclohexanol
Cyclohexanol
7
Cyclooctanol
Cyclooctanone
5
Octan-2-ol
Octan-2-one
6
aReaction conditions: alcohol (0.001 mol), PC–MnO2 nanohybrid (5 mol%, 0.04 g), p-xylene (5 ml), 80 °C, air.
bYield determined by GC analysis.
Table 5. Comparison of literature reported methods and this work for oxidation of benzyl alcohol using MnO2
Entry
Catalyst
Conditions
Ratio substrate to MnO2 by weight
Time (h)
Yield (%)
Ref.
1
2
3
4
5
MnO2/aluminium silicate
Active MnO2
CH2Cl2/reflux
1:3
12
48
4
96
77
85
95
90
[12]
[30]
Solvent free/r.t.
1:10
1:3
K-birnessiteMnO2
MnO2/Kieselguhr
PC–MnO2 nanohybrid
Toluene/O2/110 °C
Solvent free/50–55 °C/grind
p-Xylene/air/80 °C
[31]
1:2
3
[32]
1:0.05
0.5
This work
According to reported procedures,[33–35] we investigated the
formation of peroxides in the aerobic oxidation process as follows.
At 20 min before the GC analysis, excess amount of PPh3 was added
to a solution of the diphenylmethane oxidation products. The
resulting chromatogram was not different from that of sample that
was not subjected to the reduction by PPh3. These results confirm
that the mixture of products does not contain corresponding
alkylhydroperoxides as the main component. In our reaction, in
the course of aerobic oxidation, alkylperoxides are formed;
however, chitosan as a base could play an important role in
decomposing alkylhydroperoxides to ketones at relatively high
temperature (100 °C).
The stability and reusability of the catalyst were examined in
five sequential oxidation experiments for the model reaction
(Fig. 6). In fact, the PC–MnO2 nanohybrid is successfully recycled
without any significant loss of activity and selectivity. According
to FAAS analysis, MnO2 leaching is less than 0.5%.
Figure 6. Reusability of catalyst for oxidation of phenylethyl alcohol
catalysed by PC–MnO2 nanohybrid.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 154–159

Porous chitosan–MnO2 nanohybrid: a green and biodegradable catalyst
[10] C. Reed, Y. K. Lee, S. T. Oyama, J. Phys. Chem. B 2006, 110, 4207.
[11] L.-H. Huang, Y.-C. Ma, C. Zhang, Q. Wang, X.-N. Zou, J.-D. Lou, Synth.
Commun. 2011, 42, 3377.
Conclusions
A simple, safe and in situ oxidation approach was developed for the
synthesis of a uniformly dispersed PC–MnO2 nanohybrid, which
showed efficient catalytic activity for aerobic oxidation of
alkylarenes and alcohols to the corresponding carbonyl compounds
without using any additional bases and oxidants. In addition, this
protocol is highly efficient compared to earlier methods and it
requires only a catalytic amount of PC–MnO2 (5 mol%). The reactive
nature of PC–MnO2 and its recyclability allow the oxidation reactions
to proceed to higher yields with simple work-up and less waste.
[12] Q. H. Tang, S. Q. Hu, Y. T. Chen, Z. Guo, Y. Hu, Y. A. Chen, Y. H. Yang,
Micropor. Mesopor. Mater. 2010, 132, 501.
[13] R. Nie, J. Shi, S. Xia, L. Shen, P. Chen, Z. Hou, F.-S. Xiao, J. Mater. Chem. A
2012, 22, 18115.
[14] J.-D. Lou, X. L. Lu, L.-H. Huang, Q. Wang, X.-N. Zou, Synth. React. Inorg.
Metal-Org. Nano-Metal Chem. 2011, 41, 1342.
[15] A. Shaabani, Z. Hezarkhani, S. Shaabani, RSC Adv. 2014, 4, 64419.
[16] A. Shaabani, P. Mirzaei, S. Naderi, D. G. Lee, Tetrahedron 2004, 60,
11415.
[17] D. J. Macquarrie, J. J. E. Hardy, Ind. Eng. Chem. Res. 2005, 44, 8499.
[18] Z. Zarnegar, J. Safari, RSC Adv. 2014, 4, 20932.
[19] A. Shaabani, Z. Hezarkhani, E. Badali, RSC Adv. 2015, 5, 61759.
[20] A. Shaabani, A. Rahmati, Z. Badri, Catal. Commun. 2008, 9, 13.
[21] M. Mahyari, M. S. Laeini, A. Shaabani, H. Kazerooni, Appl. Organometal.
Chem. 2015, 29, 456.
[22] H. Mofakham, Z. Hezarkhani, A. Shaabani, J. Mol. Catal. A 2012,
360, 26.
[23] S. Keshipour, S. Shojaei, A. Shaabani, Cellulose 2013, 20, 973.
[24] A. Shaabani, S. Keshipour, M. Hamidzad, M. Seyyedhamzeh, J. Chem. Sci.
2014, 126, 111.
Acknowledgements
We gratefully acknowledge financial support from the Catalyst
Center of Excellence (CCE) of Shahid Beheshti University and the
Iran National Elites Foundation (INEF).
References
[25] M. Mahyari, A. Shaabani, Appl. Catal. A 2014, 469, 524.
[26] M. Mahyari, M. S. Laeini, A. Shaabani, Chem. Commun. 2014, 50,
7855.
[27] M. Mahyari, A. Shaabani, M. Behbahani, A. Bagheri, Appl. Organometal.
Chem. 2014, 28, 576.
[1] E. Roduner, W. Kaim, B. Sarkar, V. B. Urlacher, J. Pleiss, R. Gläser,
W.-D. Einicke, G. A. Sprenger, U. Beifuß, E. Klemm, C. Liebner,
H. Hieronymus, S.-F. Hsu, B. Plietker, S. Laschat, ChemCatChem. 2013,
5, 82.
[2] Z. Guo, B. Liu, Q. Zhang, W. Deng, Y. Wang, Y. Yang, Chem. Soc. Rev.
2014, 43, 3480.
[28] M. F. Zeng, X. Zhang, L. J. Shao, C. Z. Qi, X. M. Zhang, J. Organometal.
Chem. 2012, 704, 29.
[3] J.-E. Bäckvall (Ed), Modern Oxidation Methods, John Wiley, Weinheim,
[29] S. Biswas, B. Dutta, K. Mullick, C.-H. Kuo, A. S. Poyraz, S. L. Suib, ACS Catal.
2015, 5, 4394.
2011.
[4] E. Assady, B. Yadollahi, M. Riahi Farsani, M. Moghadam, Appl.
Organometal. Chem. 2015, 29, 561.
[5] M. Hajjami, L. Shiri, A. Jahanbakhshi, Appl. Organometal. Chem. 2015,
29, 668.
[30] J.-D. Lou, Z.-N. Xu, Tetrahedron Lett. 2002, 43, 6149.
[31] A. Kamimura, Y. Nozaki, S. Ishikawa, R. Inoue, M. Nakayama, Tetrahedron
Lett. 2011, 52, 538.
[32] L.-Y. Zhu, Z. Lou, J. Lin, W. Zheng, C. Zhang, J.-D. Lou, Res. Chem.
[6] A. J. Fatiadi, Synthesis 1976, 1976, 65.
Intermed. 2013, 39, 4287.
[7] B. Nammalwar, C. Fortenberry, R. A. Bunce, S. K. Lageshetty,
K. D. Ausman, Tetrahedron Lett. 2013, 54, 2010.
[8] L. M. Gandıá , M. A. Vicente, A. Gil, Appl. Catal. A 2000, 196, 281.
[9] M. M. Mohamed, I. Othman, R. M. Mohamed, J. Photochem. Photobiol. A
2007, 191, 153.
[33] G. B. Shul’pin, J. Mol. Catal. A 2002, 189, 39.
[34] G. B. Shul’pin, Y. N. Kozlov, L. S. Shul’pina, A. R. Kudinov, D. Mandelli,
Inorg. Chem. 2009, 48, 10480.
[35] G. B. Shul’pin, Y. N. Kozlov, L. S. Shul’pina, P. V. Petrovskiy, Appl.
Organometal. Chem. 2010, 24, 464.
Appl. Organometal. Chem. 2016, 30, 154–159
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc