Room-temperature catalytic oxidation of alcohols with the polyoxovanadate salt Cs5(V14As8O42Cl)

Article abstract of DOI:10.1039/c5cy01533b

While many known methods for oxidation mediated by polyoxometalates (POMs) employ environmentally friendly co-oxidants, they tend to employ large catalyst loadings (e.g. 40 mol%) and costly high reaction temperatures (~90-135 °C) that potentially contribute to the degradation of the catalyst and reduce their effectiveness. Herein, we present some initial results demonstrating a room temperature catalytic oxidation using the reduced salt-inclusion polyoxometalate, Cs₅(V₁₄As₈O₄₂Cl), that contains polyoxovanadate (POV) clusters as an efficient catalyst (e.g., 2 mol%) in the transformation of secondary alcohols to their corresponding ketones in very good to quantitative yields. Further, the catalyst can be suspended on celite and recycled.

Full text of DOI:10.1039/c5cy01533b

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Room-temperature catalytic oxidation of alcohols
with the polyoxovanadate salt Cs5IJV14As8O42Cl)†
Cite this: DOI: 10.1039/c5cy01533b
McKenzie L. Campbell, Dino Sulejmanovic, Jacqueline B. Schiller, Emily M. Turner,
*
*
Shiou-Jyh Hwu and Daniel C. Whitehead
While many known methods for oxidation mediated by polyoxometalates (POMs) employ environmentally
friendly co-oxidants, they tend to employ large catalyst loadings (e.g. 40 mol%) and costly high reaction
temperatures (~90–135 °C) that potentially contribute to the degradation of the catalyst and reduce their
effectiveness. Herein, we present some initial results demonstrating a room temperature catalytic oxidation
using the reduced salt-inclusion polyoxometalate, Cs5IJV14As8O42Cl), that contains polyoxovanadate (POV)
clusters as an efficient catalyst (e.g., 2 mol%) in the transformation of secondary alcohols to their corre-
sponding ketones in very good to quantitative yields. Further, the catalyst can be suspended on celite and
recycled.
Received 15th September 2015,
Accepted 3rd December 2015
DOI: 10.1039/c5cy01533b
www.rsc.org/catalysis
employed 5.0 equiv. of 30% aq. H2O2 as the co-oxidant. Ben-
zylic alcohols containing para-, meta-, and ortho- substituted
Introduction
Polyoxometalates (POMs) have been used rather extensively in
the past few decades as catalysts in alcohol oxidations to alde-
hydes and ketones.1–5 Of the catalysts used in these transfor-
mations, reports employing Keggin type POMs are more prev-
alent, while Wells–Dawson scaffolds are employed to a lesser
extent.6,7 Our work is focused on a complementary approach
that exploits the use of relatively unexplored reduced poly-
oxovanadates (POVs) in catalytic oxidation transformations.
electron withdrawing and donating groups, testing for both
electronic and steric effects, returned quantitative yields after
varied reaction times determined by GC analysis.
Nonactivated cyclic and aliphatic primary alcohols also gave
quantitative yields under assorted reaction times.
Work showing increased catalytic efficiency and oxidative
selectivity with tailored incorporation of vanadium–metal
ions (n = 0, 1, 2, 3) into the molybdophosphoric acid (MPA)
Keggin structure Cs2MPAVn/TiO2 shifted catalytic activation
from acid-controlled to redox-dominated oxidative processes
displayed in the selective formation of benzaldehyde with in-
creased vanadium substitution.12 A major limitation of the
catalyst system investigated is the decreased conversion of
benzyl alcohol starting material with increasing vanadium in-
corporation.12 Extending the idea of enhanced redox-capable
POM catalysts through increased vanadium substitution, a re-
cent literature review cites vanadium-substituted POMs, i.e.
hetero-transition-metal POMs,13,14 as the most extensively ex-
plored transition metal POM in the oxidation of alcohols to
aldehydes and ketones.15 Unlike the commonly explored
Keggin and Dawson POMs, including vanadium-substituted
POMs, POVs featuring exclusively vanadium as the transition-
metal cations in the POM framework, as in our catalyst struc-
ture, are largely unexplored for catalytic reactions.16
Currently,
heteropolyoxotungstates
and
hetero-
polyoxomolybdates are among the most frequently utilized
POM catalysts due to their strong Lewis acidic properties and
rich redox capabilities.8,9 For example, Zhou and co-workers
describe the dilacunary silicotungstate, K8ijγ-SiW8O36]·13H2O,
as a precatalyst with 5.0 equiv. of 30% aq. H2O2 as the co-
oxidant for the selective oxidation of activated benzylic alco-
hols as well as nonactivated aliphatic alcohols in greater than
90% yields. An elevated reaction temperature of 90 °C using
an economically feasible 0.67 mol% catalyst loading
converted most substrates investigated with the more hydro-
phobic aliphatic alcohols requiring the use of a phase-
transfer catalyst.10 A related Keggin type polyoxomolybdate,
HxPMo12O40 ⊂ H4Mo72Fe30IJCH3COO)15O245 behaves as a water
soluble nanocapsule in the selective oxidation of alcohols to
their corresponding aldehydes and ketones using 0.1 mol%
of the POM catalyst at 45 °C.11 Again this transformation
A few notable examples of vanadium-substiututed POM
catalysts do promote selective aerobic oxidations; such as
H5PV2Mo10O40 in the oxidation of benzyl alcohol to benzalde-
hyde studied in a reaction medium comprised of either poly-
ethylene glycol17 or supercritical carbon dioxide.18 While
many of these reactions feature high selectivity, acceptable
Department of Chemistry, Clemson University, Clemson, SC, 29634 USA.
E-mail: dwhiteh@clemson.edu
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5cy01533b
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yields, and utilize environmentally benign co-oxidants, some
reports of POVs requiring co-catalysts may reduce the practi-
cal utility of these methods.9c,19 POVs were reported to partic-
ipate in the catalytic oxidation of alcohols through oxygen
transfer from sulfoxides, but only in the presence of DMSO
as the solvent.20,21 The most striking limitations of current
oxidation methods promoted by POVs include high catalyst
loadings (e.g. 40 mol% in some cases)12,22 and reaction tem-
peratures ranging from 90 to 135 °C.20,23,24 Such high tem-
peratures may lead to the catalyst overheating, termed
oxide frameworks. Numerous studies have shown SIC to be
an alternative method for the creation of new porous mate-
rials via salt-inclusion, solid-state methods. The salt, like the
organic cation in their zeolite and zeolite-like counterparts,
serves as a template and due to the weak interactions at the
interface between these two chemically dissimilar lattices,
the incorporated salt can be removed by washing with
water.26,27 While the utility of SIC has been demonstrated in
the synthesis of unusually large porous frameworks (~2 nm
in pore dimension) using molten-salt synthesis, it has been
reiterated recently in the synthesis of reduced water-soluble
salt-inclusion solids containing polyoxometalate clusters.28–30
These polyoxometalate salts are soluble in water to generate
finely dispersed nanoclusters featuring a covalent metal oxide
framework with counter cations surrounding the cluster.
The study presented herein details the exploration of
several water-soluble, reduced POV salts synthesized by
means of SIC as catalysts for the selective oxidation of 2°
alcohols. Ultimately, we discovered that catalytic loadings of
the polyoxovanadate Cs5IJV14As8O42Cl) efficiently promotes the
oxidation of 2° alcohols in the presence of tert-butyl hydro-
gen peroxide (tBuOOH) as the terminal co-oxidant. Our opti-
mal conditions proceed at room temperature thus obviating
possible thermal degradation of the POV catalyst. The trans-
formation proceeds with good to excellent yields over the
course of 12 to 48 h depending upon the particular substrate.
cooking,
which
results
in
concomitant
catalyst
deactivation.15,24,25
Our interest in exploring the catalytic properties of the re-
duced POVs described herein was sparked by the significantly
different features of these materials compared to the com-
monly used POM catalysts. Given their unique electronic
state (i.e. V4+) and high negative charge, these POVs are more
basic than their fully oxidized counterparts and as such
would likely be efficient at proton abstraction from organic
alcohol substrates, which could for instance accelerate associ-
ation of the substrate with the catalyst. Specifically, the com-
position of the reduced POV that is the subject of the present
study, Cs5IJV14As8O42Cl), features (V14As8O42Cl)5− clusters in
which fourteen square pyramidal vanadium sites are reduced,
i.e. V4+. The crystal structure of Cs5IJV14As8O42Cl) is
manifested through the artwork shown in Fig. 1, where the
mixed arsenicIJIII)-POV cluster [V4+14As3+8O42Cl]5− is residing in
the Cs+-based half sodalite (SOD) β-cage. The compound is
soluble in water, due to the ionic interaction at the interface
of this composite framework, and it forms micron-size
(V14As8O42Cl)5− aggregates in aqueous solution (vide infra).
Each of the catalytically active vanadium atomic sites features
apical vanadyl (V4+ = O) short oxygen bonds pointing away
from the center of the cluster.
Results & discussion
We elected to evaluate the catalytic potential of three POV
catalysts that were prepared by the salt-inclusion method:
Cs3.5Na1.47IJV5O9)IJAsO4)2Cl2.33 (1),28 Cs5IJV14As8O42Cl) (2),29 and
Cs11Na3Cl5IJV15O36Cl) (3).30 These catalysts were prepared
analogous
to
the
method
described
below
for
With regards to the synthesis of these POV catalysts, we
have been employing the newly emerged salt-inclusion chem-
istry (SIC), which has been developed in our laboratories to
yield a collection of novel composite materials featuring an
integrated composite lattice of ionic salts and covalent metal
Cs5IJV14As8O42Cl). POV 2 was synthesized by employing a
slightly modified stoichiometric reaction compared to previ-
ously reported conditions.29 Briefly, CsCl, Cs3VO4, As2O3,
V2O3 and VO2 were loaded in a 3 : 4 : 12 : 2 : 34 molar ratio
(0.75 g total mass), respectively, and employing procedures
Fig. 1 Representation of the (V14As8O42Cl)5− cluster (left) residing in the Cs+-based half SOD β-cage (middle) to form a partial structure of the
composite lattice (right) of the water-soluble Cs5IJV14As8O42Cl).
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described in literature returned a dark brown polycrystalline
powder that was ground and was subjected to powder X-ray
diffraction to confirm the phase formation (Fig. S1†).
conditions of 2 mol% catalyst loading with 5 equiv. of aque-
ous tBuOOH in acetone [0.25 M] for 12 hours at room tem-
perature allowed for 100% conversion of the starting material
to product. Lowering the equivalents of co-oxidant as low as
1.5 equiv. did not drastically affect the yield of the reaction
(entries 11 and 12). Nonetheless, when the loading of
Cs5IJV14As8O42Cl) was reduced below 2 mol%, a large reduc-
tion in yield was observed (entries 13 and 14). Given that the
reaction proceeded at significantly improved yield in acetone,
we wondered whether the POV might merely serve as a coor-
dination site to facilitate the well-known Oppenauer oxida-
tion.31,32 To rule out a possible Oppenauer-like transforma-
tion, we investigated the transformation of 4 to 5 in the
presence of catalyst 2 without the addition of co-oxidant
(entries 15 and 16). In both acetone and aqueous acetone
solvent systems, acetophenone 5 was isolated in 7% yield in
the absence of tBuOOH. These results clearly indicated that
the oxidation of 2-phenylethanol by means of acetone is not
favorable in the presence of POV 2 catalyst. Next, we wished
to rule out the notion that the observed oxidation might be
mediated by atmospheric oxygen. Conducting the reaction
under anoxic conditions (i.e. under dry N2) did not reduce
the yield of acetophenone product (entry 17). Further, conducting
the reaction under an oxygen atmosphere (i.e. 1 atm, O2 bal-
loon) in the absence of tBuOOH failed to return acetophen-
one product (entry 18). Taken together these two results clearly
indicate that POV 2 is not catalytically competent under aero-
bic conditions without the addition of a suitable co-oxidant.
For our initial investigation, we probed the ability of cata-
lysts 1–3 (0.05 equiv.) to promote the oxidation of
1-phenylethanol (4) to acetophenone (5) in water in the pres-
ence of 1.5 equiv. of aqueous tBuOOH as a terminal co-oxi-
dant. The reactions were conducted at room temperature for
24 h and monitored by GC in triplicate (Table 1, entries 1–3).
Product GC peak areas were correlated to yield by means of
standard curves (see ESI†). The yields appearing in Table 1
are averages of triplicate runs. Among the three POV cata-
lysts, Cs5IJV14As8O42Cl) (2, entry 2) returned the desired prod-
uct in 36% yield. In all cases, the POV catalysts outperformed
the uncatalyzed background reaction mediated by aqueous
tBuOOH alone (15% yield, entry 4). Based on these initial re-
sults, we elected to pursue the optimization of the reaction
catalyzed by Cs5IJV14As8O42Cl) (2).
Increasing the loading of the co-oxidant to 5 equiv. led to
an increase in yield to 62% of 5 (entry 5). Other common ter-
minal co-oxidants, including aqueous hydrogen peroxide,
Oxone®, and urea–hydrogen peroxide complex (UHP) were in-
ferior, returning 5 in 7%, 15%, and 5% yields, respectively
(entries 6–8). Omitting the inclusion of additional water, the
ketone was recovered in 60% yield (entry 9). Conducting the
reaction in acetone (entry 10) led to a significant break-
through culminating in an optimized protocol that returned
quantitative yields of acetophenone (5). Thus, optimized
Table 1 Optimization of catalytic oxidation of 1-phenylethanol using 2 mol% catalytic Cs5IJV14As8O42Cl)
Entry
Catalyst (equiv.)
Solventa [M]
Co-oxidant (equiv.)
Time
Yield (%)
1
2
3
4
5
6
7
8
Cs3.5Na1.47IJV5O9)IJAsO4)2Cl2.33 (0.05) (1)
Cs5IJV14As8O42Cl) (0.05) (2)
Cs11Na3Cl5IJV15O36Cl) (0.05) (3)
None
H2O [0.3]
H2O [0.3]
H2O [0.3]
H2O [0.3]
H2O [0.3]
H2O [0.3]
H2O [0.3]
H2O [0.3]
TBHPb (aq.) (1.5)
TBHP (aq.) (1.5)
TBHP (aq.) (1.5)
TBHP (aq.) (1.5)
TBHP (aq.) (5.0)
H2O2c (aq.) (5.0)
Oxone® (5.0)
UHP (5.0)
TBHP (aq.) (5.0)
TBHP (aq.) (5.0)
TBHP (aq.) (1.5)
TBHP (aq.) (3.0)
TBHP (aq.) (5.0)
TBHP (aq.) (5.0)
H2Od
24 h
24 h
24 h
24 h
24 h
24 h
24 h
24 h
24 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
28%
36%
22%
15%
4
8
2
3
Cs5IJV14As8O42Cl) (0.05)
Cs5IJV14As8O42Cl) (0.05)
Cs5IJV14As8O42Cl) (0.05)
Cs5IJV14As8O42Cl) (0.05)
Cs5IJV14As8O42Cl) (0.05)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.01)
Cs5IJV14As8O42Cl) (0.005)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.02)
Cs5IJV14As8O42Cl) (0.02)
62% 13
7%
13%
5%
60%
100%
87%
95%
62%
47%
7%
3
0
1
8
3
5
2
4
2
0
0
1
2
9
—
10
11
12
13
14
15
16
17e
18f
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
Acetone [0.25]
None
TBHP (aq.) (5.0)
None
7%
100%
6%
a
b
c
[M] = (0.1 mmol starting material/x mL solvent). TBHP (aq.) denotes a 70% aq. solution of TBHP employed as a co-oxidant. H2O2 (aq.)
denotes a 30% aq. solution of H2O2 employed as a co-oxidant. Equal volume to TBHP. e Ran under N2. Ran under O2 ballon.
d
f
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Next, we turned to an investigation of the substrate scope
could be easily overcome by increasing the catalyst loading to
10 mol% for 48 h. Using these optimized conditions for ali-
phatic ketones, the yield of 20 was raised to 97%. Similarly,
2-octanol returned 67% of the product 22 when using
10 mol% of the POV catalyst. A higher 79% yield of 22 was
realized at 2 mol% catalyst loading, albeit after 5 d.
for the transformation of secondary alcohols to their corre-
sponding ketones (Fig. 2). Similar to the quantitative conver-
sion of 1-phenylethanol (4) to acetophenone (5), a number of
other substituted benzylic alcohols were readily oxidized to
their corresponding ketone products (i.e. 6–13), in excellent
yields ranging from 90% to quantitative, regardless of the
electronic nature of the arene substituent. The cyclopropyl
substituted ketone 14 was recovered in a good yield of 87%
while both the heterocyclic pyridine and furyl-activated alco-
hols gave modest yields of 15 in 62% and 16 in 68%. The
successful preparation of ketone 14 from the corresponding
cyclopropyl substituted benzyl alcohol is particularly note-
worthy. Specifically, the survival of the cyclopropyl moiety in
14 strongly suggests that the process is governed by a two
electron oxidation in lieu of a radical mediated process that
would likely result in the rupture of the strained cycloalkane
to give an allyl radical. The spirocyclic ketone 17 was regretta-
bly recovered in only a 20% yield, and significant decomposi-
tion of the substrate was noted with either 2 or 10 mol% cat-
alyst. Oxidation 2-cyclohexenol returned the α,β-unsaturated
ketone 18 in a moderate 66% yield, while oxidation of the
more sterically encumbered (−)-carveol lead to a disappoint-
ing ~30% of carvone 19 with both 2 and 10 mol% catalyst.
Unfortunately, the yield could not be further improved with
prolonged reaction time. Gratifyingly, the non-activated 2°
alcohol cyclohexanol returned cyclohexanone (20) in 89%
yield. Disappointingly, however, the oxidation of 4-heptanol
returned the corresponding ketone 21 in a 70% yield after an
impractical 5 day reaction time. Nevertheless, this limitation
Next, we investigated the oxidation of benzyl alcohol (23)
(Fig. 3), which returned a mixture of 24% benzaldehyde (24)
and 20% benzoic acid (25) after 24 h, along with unreacted
starting material. After 72 h, however, no benzaldehyde (24)
was present via GC analysis and a 46% yield of the benzoic
acid (25) was recovered. Using benzaldehyde as the starting
material under the optimized conditions returned roughly
40% of 25 as well. Substituting the electron withdrawing
trifluromethyl group at the para-position of the aryl ring
(Fig. 3, 26) did enhance conversion of the starting material.
However, substitution of an electron donating para-methoxy
(p-OMe) allowed for a full conversion of the starting alcohol
with selectivity for the acid product 31 in a 92% yield while
the aldehyde product 30 was recovered in a 12% yield.
Cinnamyl alcohol gave 35% conversion to cinnamic acid 34.
Nevertheless, this reaction was accompanied by significant
degradation of the starting alcohol. While 1° benzylic systems
are subject to oxidation (albeit rather unselectively) under our
optimized conditions, attempted conversion of unactivated
1-octanol resulted in complete recovery of starting material.
Further, treatment of cyclohexane under the optimized condi-
tions for 72 h returned only 2% cyclohexanone (20), and no
detectable cyclohexanol, indicating that our standard condi-
tions are not amenable for alkane C–H activation.
Fig. 2 Substrate scope for secondary alcohols. a48 h reaction time. b10 mol% of POV catalyst used. c5d reaction time.
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Fig. 3 Catalytic oxidation of benzyl alcohol and derivatives using 2 mol% Cs5IJV14As8O42Cl). a24h reaction time.
Finally, we sought to evaluate whether the catalyst was recy-
clable. In order to facilitate catalyst recovery, Cs5IJV14As8O42Cl)
was impregnated on celite (see ESI† for details). In doing so,
the catalyst could be readily recovered after a simple filtra-
tion step. Fig. 4A clearly indicates that the impregnated
catalyst can be recycled up to three times in the oxidation of
1-phenylethanol (4) without any detectable reduction in iso-
lated yield of acetophenone product on a 1 mmol scale.
Nevertheless, further attempts at recycling lead to reduced
yields of 5. Fig. 4B illustrates a qualitative light-scattering ex-
periment (using
a green laser) that suggests that the
Cs5IJV14As8O42Cl) molecules readily form micron size aggre-
gates in solution. Further, these aggregates are maintained
throughout the entire course of the oxidative transformation.
This experiment may be taken as qualitative evidence that
the POV maintains its structural integrity throughout the cat-
alytic cycle. We are currently pursuing more quantitative
means to verify this supposition, and the results of these
studies will be reported in due course.
Conclusion
In conclusion, we demonstrated the use of the poly-
oxovanadate, Cs5IJV14As8O42Cl) (2), as a catalyst for the selec-
tive oxidation of secondary alcohols to ketones at room tem-
perature with as little as 2 mol% of the catalyst. The use of
finely dispersed POV clusters avoids current limitations with
oxidation methods promoted by POVs including high catalyst
loadings (e.g. 40 mol%)12,22 and reaction temperatures
ranging from 90 to 135 °C.20,23,24 The conversion of
1-phenylethanol (4) to acetophenone (5) proceeded at quanti-
tative conversions at both a 0.1 and 1.0 mmol scale. Other
substituted 2° benzylic alcohols were oxidized in good to
excellent yields. The catalyst also effectively oxidizes 2° alkyl
Fig. 4 (A) Scalable regeneration of Cs5IJV14As8O42Cl) catalyst isolated
and reused consecutively over three reactions. (B) Light scattering
experiment showing the aggregation of the Cs5V14As8O42Cl clusters in
solution from left to right; 1. acetone 2. acetone + POV 3. acetone +
POV + substrate + TBHP 4. acetone + POV + substrate + TBHP after
15 minute stir.
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alcohols, albeit at higher (i.e. 10 mol%) catalyst loadings.
Further efforts to understand the mechanism of the transfor-
mation as well as to expand the synthetic utility of these
novel POV catalysts are underway.
Chen, R. Tan, W. Zheng, Y. Zhang, G. Zhao and D. Yin,
Catal. Sci. Technol., 2014, 4, 4048–4092.
9 (a) M. Misono, Chem. Commun., 2001, 1141–1152; (b) R. Ben-
Daniel and R. Neumann, Angew. Chem., Int. Ed., 2013, 42,
92–95; (c) R. Ben-Daniel, P. Alsters and R. Neumann, J. Org.
Chem., 2001, 66, 8650–8653; (d) L. M. Dornan and M. J.
Muldoon, Catal. Sci. Technol., 2015, 5, 1428–1432; (e) X.
Huang, X. Zhang, D. Zhang, S. Yang, X. Feng, J. Li, Z. Lin, J.
Cao, R. Pan, Y. Chi, B. Wang and C. Hu, Chem. – Eur. J.,
2014, 20, 2557–2564.
Acknowledgements
We would like to thank the Clemson University Chemistry
Department for their support.
10 B. Ma, Y. Zhang, Y. Ding and W. Zhao, Catal. Commun.,
2010, 11, 853–857.
References
1 I. V. Kozhevnikov, V. E. Taraban'ko and K. I. Matveev, Dokl.
Akad. Nauk SSSR, 1977, 235, 1347–1349.
11 E. Nikbakht, B. Yadollahi and M. R. Farsani, Inorg. Chem.
Commun., 2015, 55, 135–138.
2 K. Nomiya, Y. Sugie, T. Miyazaki and M. Miwa, Polyhedron,
1986, 5, 1267–1271.
3 R. Neumann, A. M. Khenkin, D. Juwiler, H. Miller and M.
Gara, J. Mol. Catal. A: Chem., 1997, 117, 169–183.
4 H. Firouzabadi, N. Iranpoor and K. Amani, Synthesis,
2003, 3, 408–412.
5 Y. Leng, P. Zhao, M. Zhang and J. Wang, J. Mol. Catal. A:
Chem., 2012, 358, 67–72.
12 P. S. N. Rao, G. Parameswaram, A. V. P. Rao and N.
Lingaiah, J. Mol. Catal. A: Chem., 2015, 399, 62–70.
13 V. Palermo, P. I. Villabrille, P. G. Vazquez, C. V. Caceres, P.
Tundo and G. P. Romanelli, J. Chem. Sci., 2013, 125, 1375–1383.
14 P. S. N. Rao, K. T. Venkateswara Rao, P. S. Sai Prasad and N.
Lingaiah, Catal. Commun., 2010, 11, 547–550.
15 S. Wang and G. Yang, Chem. Rev., 2015, 115, 4893–4962.
16 K. Y. Monakhov, W. Bensch and P. Kogerler, Chem. Soc. Rev.,
2015, 44, 8443–8483.
17 A. Haimov and R. Neumann, Chem. Commun., 2002, 876–878.
18 G. Maayan, B. Ganchegui, W. Leitner and R. Neumann,
Chem. Commun., 2006, 2230–2232.
19 R. Neumann, A. M. Khenkin and I. Vigdergauz, Chem. – Eur.
J., 2000, 6, 875–882.
20 A. M. Khenkin, G. Leitus and R. Neumann, J. Am. Chem.
Soc., 2010, 132, 11446–11448.
21 A. M. Khenkin and R. Neumann, J. Org. Chem., 2002, 67,
7075–7079.
22 A. Bordoloi, S. Sahoo, F. Lefebvre and S. B. Halligudi,
J. Catal., 2008, 259, 232–239.
23 T. Okuhara, Chem. Rev., 2002, 102, 3641–3666.
24 L. Jing, J. Shi, F. Zhang, Y. Zhong and W. Zhu, Ind. Eng.
Chem. Res., 2013, 52, 10095–10104.
25 I. V. Kozhevnikov, J. Mol. Catal. A: Chem., 2007, 262, 86.
26 J. P. West and S.-J. Hwu, J. Solid State Chem., 2012, 195,
101–107.
27 Q. Huang, M. Ulutagay, P. A. Michener and S.-J. Hwu, J. Am.
Chem. Soc., 1999, 121, 10323–10326.
28 W. L. Queen, S.-J. Hwu and S. Reighard, Inorg. Chem.,
2010, 49, 1316–1318.
29 W. Queen, J. P. West, S.-J. Hwu, T. T. Tran, P. S.
Halasyamani and D. VanDerveer, Chem. Commun., 2012, 48,
1665–1667.
6 (a) Y. Kikukawa, K. Yamaguchi and N. Mizuno, Angew.
Chem., Int. Ed., 2010, 49, 6096–6100; (b) J. Wang, L. Yan, G.
Li, X. Wang, Y. Ding and J. Suo, Tetrahedron Lett., 2005, 46,
7023–7027; (c) P. Tundo, G. P. Romanelli, P. G. Vazquez and
F. Arico, Catal. Commun., 2010, 11, 1181–1184; (d) W. Zhao,
Y. Zhang, B. Ma, Y. Ding and W. Qiu, Catal. Commun.,
2010, 11, 527–531; (e) Y. Ding and W. Zhao, J. Mol. Catal. A:
Chem., 2011, 337, 45–51; ( f ) C. N. Kato, A. Tanabe, S.
Negishi, K. Goto and K. Nomiya, Chem. Lett., 2005, 34,
238–239; (g) A. Yokoyama, K. Ohkubo, T. Ishizuka, T.
Kojima and S. Fukuzumi, Dalton Trans., 2012, 41,
10006–10013; (h) J. Wang, L. Yan, G. Qian, G. Lv, G. Li, J.
Suo and X. Wang, React. Kinet. Catal. Lett., 2007, 91,
111–118; (i) S. Hasannia and B. Yadollahi, Polyhedron,
2015, 99, 260–265; ( j) S. Pathan and A. Patel, Catal. Sci.
Technol., 2014, 4, 648–656.
7 (a) M. R. Farsani, F. Jalilian, B. Yadollahi and H. A. Rudbari,
Polyhedron, 2014, 76, 102–107; (b) J. H. Choi, J. K. Kim, S.
Park, J. H. Song and I. K. Song, Appl. Catal., A, 2012, 427–
428, 79–84; (c) D. R. Park, H. Kim, J. C. Jung, S. H. Lee and
I. K. Song, Res. Chem. Intermed., 2008, 34, 845–851; (d) J. H.
Choi, T. H. Kang, Y. Bang, J. H. Song and I. K. Song, Catal.
Commun., 2014, 55, 29–33; (e) M. Masteri-Farahani, G. R.
Najafi, M. Modarres and M. Taghvai-Nakhjiri, J. Porous
Mater., 2015, Ahead of Print.
8 (a) I. V. Kozhevnikov, Chem. Rev., 1998, 98, 171–198; (b) Y.
Ding, W. Zhao, Y. Zhang, B. Ma and W. Qiu, React. Kinet.,
Mech. Catal., 2011, 102, 85–92; (c) M. R. Farsani, E. Assady,
F. Jalilian, B. Yadollahi and H. A. Rudbari, J. Iran. Chem.
Soc., 2015, 12, 1207–1212; (d) M. R. Farsani and B.
Yadollahi, J. Mol. Catal. A: Chem., 2014, 392, 8–15; (e) Y.
30 W. L. Queen, J. P. West, J. Hudson and S.-J. Hwu, Inorg.
Chem., 2011, 50, 11064–11068.
31 R. V. Oppenauer, Recl. Trav. Chim. Pays-Bas, 1937, 56,
137–144.
32 E. J. Creyghton and J. C. van der Waal, Stud. Surf. Sci. Catal.,
2001, 438–448.
Catal. Sci. Technol.
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