Preparation of clay-supported Sn catalysts and application to Baeyer-Villiger oxidation

Article abstract of DOI:10.1039/c2gc16437j

Clay-intercalated Sn catalysts were prepared by a conventional cation-exchange method and used for the Baeyer-Villiger oxidation of various ketones with hydrogen peroxide as an oxidant. The intercalation of monomeric Sn species into the clay interlayer was monitored by solid-state ⁷Li MAS NMR. Solid-state ¹¹⁹Sn MAS NMR and Sn K-edge XAFS analysis revealed that an isolated Sn species, such as [Sn^IV(OH)_x(H ₂O)_5-x]^(4-x)+ (x = 0-3), was formed in the clay interlayers. Our clay-intercalated Sn catalysts showed extremely high performance in Bayer-Villiger oxidation and were also reusable without any significant loss of activity or selectivity. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2gc16437j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Green Chemistry
Cite this: Green Chem., 2012, 14, 771
www.rsc.org/greenchem
PAPER
Preparation of clay-supported Sn catalysts and application to Baeyer–Villiger
oxidation†
Takayoshi Hara, Moriaki Hatakeyama, Arum Kim, Nobuyuki Ichikuni and Shogo Shimazu*
Received 11th November 2011, Accepted 16th December 2011
DOI: 10.1039/c2gc16437j
Clay-intercalated Sn catalysts were prepared by a conventional cation-exchange method and used for the
Baeyer–Villiger oxidation of various ketones with hydrogen peroxide as an oxidant. The intercalation of
monomeric Sn species into the clay interlayer was monitored by solid-state 7Li MAS NMR. Solid-state
119Sn MAS NMR and Sn K-edge XAFS analysis revealed that an isolated Sn species, such as
[SnIV(OH)x(H2O)5−x (4−x)+ (x = 0–3), was formed in the clay interlayers. Our clay-intercalated Sn
]
catalysts showed extremely high performance in Bayer–Villiger oxidation and were also reusable without
any significant loss of activity or selectivity.
Lithium taeniolite (Li/TN) of fluorotaeniolite type mica is
Introduction
composed of negatively charged layers between which there are
lithium cations. The structure of Li/TN is built by stacking
complex layers made of two SiO4 octahedral sheets and one
(Mg,Li)O6 octahedral sheet.7 These stacked layers are connected
with interlayer sheets made up of exchangeable Li+ cations and
water molecules in the Li/TN matrix. With Li/TN as a host com-
pound, we have already reported that various intercalated metal
complex catalysts selectively promote various organic transform-
ations.8 In particular, TN-intercalated zirconium complexes
efficiently catalyzed the ring-opening reaction of terminal oxi-
ranes with various alcohols and carboxylic acids because of
their Lewis acidity.8d,e We are now focusing on designing high-
performance heterogeneous catalysts with isolated and uniform
active species by a simple cation-exchange reaction between the
clay host and interlayer guest cations.
In this paper, we wish to present the synthesis and characteris-
ation of a TN-intercalated Sn catalyst and its evaluation as a het-
erogeneous catalyst for the Baeyer–Villiger oxidation of cyclic
ketones using aqueous hydrogen peroxide. The highly dispersed
isolated SnIV species in the TN interlayer has proven to be effec-
tive as a catalytically active species for selective and environ-
mentally benign Baeyer–Villiger oxidation.
The Baeyer–Villiger oxidation is the most widely applied reac-
tion in organic synthesis.1 Through this oxidation reaction, a
variety of carbonyl compounds, such as ketones, cyclic ketones,
benzaldehydes, and carboxylic acids, can be transformed into
various oxidised products, such as esters, lactones, phenols,
and anhydrides, respectively.2 Although many types of homo-
geneous, heterogeneous, and enzyme catalysts have been
reported for the Baeyer–Villiger oxidation, the reactions using
these catalysts are often carried out with expensive, hazardous
peracids, including in situ generated organic peroxides formed
from aldehydes and molecular oxygen, leading to the formation
of one equivalent of the corresponding carboxylic acid.3 From
the viewpoint of green and sustainable chemistry, many attempts
to develop a heterogeneous catalytic system with hydrogen per-
oxide as the sole oxidant have been made.4
In 2001, Corma and his co-workers reported that Sn-contain-
ing beta zeolite (Sn-β-zeolite) has become one of the most effec-
tive catalysts for the Baeyer–Villiger oxidation reaction with
hydrogen peroxide.5a Based on the analyses using various
characterisation techniques, it was revealed that the Lewis acidity
of isolated tetrahedral SnIV species activates the carbonyl group
of substrates. In addition, various types of heterogeneous cata-
lysts, including Sn species such as Sn-dendrimer/polystyrene,6a
Sn-MCM-14,6b Sn/cellulose,6c Sn/polystyrene,6d and Sn-contain-
ing clay minerals such as hydrotalcite,6e palygorskite,6f and
montmorillonite,6g have been developed in the past decade.
Results and discussion
The chemical composition of Li/TN is ideally Li[(Mg2Li)
(Si4O10)F2] and its cation exchange capacity (CEC) is
268.2 meq/100 g. Intercalation of Sn species into TN interlayers
was achieved by a simple cation exchange process using
SnCl2·2H2O as a precursor. SnCl2·2H2O is able to dissolve into
a CH3OH/water solution, giving a clear, colourless solution. In
general, tin cations are easily transformed into insoluble tin
hydroxide in water via hydrolysis of coordinated water mol-
ecules, because of its high Lewis acidity. It might be said that
the hydrolysis, which leads to the formation of insoluble tin
Department of Applied Chemistry and Biotechnology, Graduate School
of Engineering Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522,
Japan. E-mail: shimazu@faculty.chiba-u.jp; Fax: +81-43-290-3379;
Tel: +81-43-290-3379
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c2gc16437j
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 771–777 | 771

View Article Online
Table 1 Results of chemical analyses of Sn(X)/TN catalysts
Catalyst
Li/TN
Sn(0.19)/TN 7.20
Sn(0.40)/TN 5.98
Sn(0.77)/TN 5.84
d001 (degree) BS (nm)a CS (nm)b LA (mmol g−1 c
)
7.36
1.20
1.23
1.48
1.51
0.24
0.27
0.52
0.55
—
0.19
0.40
0.77
a Basal spacing. b Clearance space = BS − thickness of layer (0.96 nm).
c Loading amount of Sn species determined by ICP analysis.
hydroxide, is inhibited by the addition of CH3OH, and a stable
Sn complex is formed.
Three classes of TN-intercalated Sn catalysts are synthesised
by varying the Sn loading amount (0.19, 0.40, or 0.77 mmol
g−1), and the result of the chemical analysis are shown in
Table 1. The synthesised catalysts are denoted Sn(X)/TN (the
number in parentheses indicates the loading amount of the Sn
species in mmol g−1). Powder X-ray diffraction (XRD) profiles
revealed that Sn(0.19)/TN and the parent Li/TN had almost the
same layered structures, and their CS values (clearance space =
basal spacing − thickness of layer (0.96 nm)) were 0.27 and
0.24 nm, respectively.9 The CS increased with increasing
loading amount of Sn species, and Sn(0.77)/TN catalyst had a
CS of up to 0.55 nm.
Fig. 2 Relation between 7Li MAS NMR signal and loading amount of
Sn species.
(0 ppm). As can be clearly observed, two peaks at −0.2 and
−0.7 ppm appeared in the spectrum of a Li/TN sample (Fig. 1a).
This result strongly supports the Li+ cations situate themselves at
two crystallographic sites, i.e., the Li+ cations exist as exchange-
able interlayer Li+ cations and framework Li+ cations in an octa-
hedral sheet, as reported by Toraya and coworkers.7 With the
intercalation of the Sn species, the intensity of the peak at
To confirm the progress of the cation exchange reaction, the
7
TN-intercalated Sn catalysts were analysed by Li magic-angle-
spinning (MAS) nuclear magnetic resonance (NMR) (Fig. 1).
7
Because of its high gyromagnetic ratio, γ(7Li)/γ(1H) = 0.389,
−0.3 ppm decreased slightly (Fig. 1b–d). For the results of Li
7
MAS NMR, it should be noted that the peaks around −0.2 and
−0.6 ppm correspond to the interlayer exchangeable Li+ cations
and the framework Li+ cations in the octahedral sheets, respect-
ively.12 The area ratio of the interlayer Li+ peak to the framework
and its natural abundance (92.58%), Li is a powerful probe for
experimental studies exploiting this NMR technique.10 More-
7
over, Li is very sensitive to the asymmetry of its electrostatic
environment because of its quadrupolar nucleus with 3/2 spin.11
The chemical shift was referenced to LiCl as an external standard
7
Li+ peak in the Li MAS NMR spectra is inversely proportional
to the loading amount of Sn species (Fig. 2), indicating the inter-
calation of Sn species into a TN interlayer occurs via a cation
exchange reaction.
The local structure of Sn species in the TN interlayer was
investigated with 119Sn MAS NMR and Sn K-edge X-ray
absorption fine structure (XAFS) spectroscopy. It is well known
that there are three Sn isotopes: 115Sn (0.35%), 117Sn (7.67%),
and 119Sn (8.58%), which all possess a nuclear spin of 1/2.13 In
particular, 119Sn NMR signals are detectable owing to the large
sensitivity associated with the spin 1/2 of the 119Sn nucleus.14
The chemical shift was referenced to (CH3)4Sn as an external
standard (0 ppm). For the crystalline SnO2 sample (Fig. 3a),
there was one sharp resonance at −604 ppm, in accordance with
the cassiterite structure, in which there is one Sn site per unit cell
and SnIV is in almost regular octahedral surroundings.15,16 The
spectrum of the SnO sample is made up of many peaks because
of the very strong Sn–Sn coupling constant (Fig. 3b).16 In the
case of TN-intercalated Sn catalysts, a broad peak at −604 ppm
was observed (Fig. 3c–e), suggesting that the Sn species in the
TN interlayer do not have the same structure as bulk SnO2 but
instead have a different distribution of Sn–O coordination
numbers, bond angles, and bond lengths. Furthermore, the broad
signals of TN-intercalated Sn catalysts might be due to various
factors, such as a low concentration and the crystallinity of Sn
species or the different natures of substituents of Sn.
Fig. 1 7Li MAS NMR spectra of (a) Li/TN, (b) Sn(0.19)/TN, (c)
Sn(0.40)/TN, and (d) Sn(0.77)/TN catalyst, collected at a spinning rate
of 20 kHz.
772 | Green Chem., 2012, 14, 771–777
This journal is © The Royal Society of Chemistry 2012

View Article Online
Fig. 3 119Sn MAS NMR spectra for (a) SnO2, (b) SnO, (c) Sn(0.77)/
TN, (d) Sn(0.40)/TN, and (e) Sn(0.19)/TN catalyst, collected at a spin-
ning rate of 20 kHz. The asterisk denotes spinning sidebands.
Fig. 5 FT of k3-weighted Sn K-edge EXAFS for (a) Sn(0.19)/TN, (b)
Sn(0.40)/TN, (c) Sn(0.77)/TN, (d) SnO2, (e) SnCl4·5H2O, (f) SnO, and
(g) SnCl2·2H2O.
In the Sn K-edge X-ray absorption near-edge structure
(XANES) spectrum, the edge energy of the TN-intercalated Sn
catalysts did not resemble that of SnCl2·2H2O or SnO but were
similar to those of SnCl4·5H2O and SnO2 (Fig. 4). This simi-
larity suggests that tetravalent Sn species are present in the TN
interlayer. The Fourier transform (FT) of the k3-weighted Sn K-
edge extended X-ray absorption fine structure (EXAFS) data is
shown in Fig. 5. For the TN-intercalated Sn catalysts, the Sn–Cl
bond peak at approximately 0.21 nm was not observed (Fig. 5a–
c). Furthermore, the peaks observed for the SnO or SnO2 corre-
sponding to the Sn–(O)–Sn bond were not observed in the
second coordination sphere (Fig. 5d–g). Thus, aggregated Sn
species, such as SnO or SnO2, are not present in the TN
interlayers.
In the case of TN-intercalated Sn catalysts, the peak in the
range of ca. 0.1–0.2 nm in Fig. 5a was well fitted by using the
Sn–O shell parameters.17 The curve-fitting analysis of the
Sn(0.19)/TN catalyst suggested that five oxygen atoms at
0.205 nm were coordinated to the monomeric SnIV centre
(Table 2).18 The distances from the Sn atoms to the nearest
Table 2 Curve-fitting results of Sn K-edge EXAFS for various TN-
intercalated Sn catalystsa
Sample
Shell
CNc
R (nm)d
σ (nm)e
b
SnO2
Sn–O
(6)
(2)
(8)
5.4
4.6
4.8
(0.206)
(0.318)
(0.371)
0.205
0.205
0.206
Sn–(O)–Sn
Sn–(O)–Sn
Sn–O
Sn–O
Sn–O
Sn(0.19)/TN
Sn(0.40)/TN
Sn(0.77)/TN
0.0077
0.0055
0.0079
a Curve-fitting analysis was performed in k-space with the inverse FT of
the 0.092 nm < r < 0.196 nm range using SnO2 as a standard material.
b Data from X-ray crystallography. c Coordination number. d Bond
distance. e σ is Debye–Waller factor.
Fig. 4 Sn K-edge XANES spectra for (a) Sn(0.19)/TN, (b) Sn(0.40)/
TN, (c) Sn(0.77)/TN, (d) SnO2, (e) SnCl4·5H2O, (f) SnO, and (g)
SnCl2·2H2O.
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 771–777 | 773

View Article Online
oxygen atoms were essentially consistent with the values deter-
catalyst was removed by hot filtration after the oxidation of
cyclopentanone reached almost 50% conversion. After removal
of the catalyst, the reaction was monitored for 120 min, and
additional formation of δ-valerolactone was not observed.9
These results show that the reaction proceeds on the TN inter-
layer and that leaching of the dissolved Sn species does not
occur under the reaction conditions.
mined by X-ray crystallography for the Sn–O bond (R =
7
0.206 nm) in SnO2.19 Based on the results of the Li and 119Sn
MAS NMR and Sn K-edge XAFS, we propose that the local
structure of the Sn species in the TN interlayers is an isolated
[SnIV(OH)x(H2O)5−x (4−x)+ (x = 0–3) species.
]
To investigate the catalytic abilities of the Sn(0.77)/TN, the
Baeyer–Villiger oxidation of cyclopentanone with aqueous H2O2
at 80 °C was carried out as a model reaction. It is noteworthy
that the use of 0.05 g of the Sn(0.77)/TN catalyst (Sn content:
0.0385 mmol) in 1,2-dichloroethane (1,2-DCE: 1.5 mL) allowed
cyclopentanone (0.5 mmol) to react with aqueous H2O2 (2 eq.
relative to the ketone) in a highly effective manner, giving a
quantitative yield of δ-valerolactone in 2 h (Table 3, entry 1).20
No oxidation proceeded in the absence of the catalyst or in the
presence of the Li/TN catalyst. The Sn(0.77)/TN catalyst showed
a high performance for oxidising various ketones using H2O2 as
the sole oxidant, as is summarised in Table 3. Cyclohexanone
and 4-methyl cyclohexanone were converted to the correspond-
ing lactones, such as ε-caprolactone and γ-methyl-ε-caprolac-
tone, respectively, with an excellent yield (entries 4 and 5).
Sterically hindered 2-adamantanone and aliphatic 4-methyl-2-
pentanone also acted as good substrates, giving a quantitative
yield of 4-oxahomoadamantane-5-one and a 72% yield of 2-
methylpropyl acetate, respectively (entries 6 and 7). After the
oxidation, the spent Sn(0.77)/TN catalyst was easily separated by
simple filtration. The recovered catalyst could be reused without
additional treatment, and its high activity and selectivity were
maintained (entries 2 and 3).21 The amount of Sn species that
leached into the reaction solution was sufficiently small to be
undetectable by ICP analysis. To further demonstrate the require-
ment of the heterogeneous Sn(0.77)/TN catalyst, the solid
The most notable feature of catalytic Baeyer–Villiger oxi-
dation with H2O2 mediated by Sn(0.77)/TN was that cyclopenta-
none was able to be transformed into δ-valerolactone specifically
with 99% selectivity and 99% efficiency with respect to H2O2
utilisation, as highlighted in Scheme 1.
The effect of the Sn loading amount on the Baeyer–Villiger
oxidation of cyclopentanone using various TN-intercalated Sn
catalysts was explored (Table 4). The catalytic activity increased
as the loading amount of Sn decreased, despite the narrow CS.
The Sn(0.19)/TN catalyst showed the highest catalytic activity,
and only δ-valerolactone, in an almost quantitative yield, was
formed (entry 3). Among the other Sn compounds examined as
catalysts, SnO, SnO2, Sn(OH)4, SnCl2·2H2O, and SnCl4·5H2O
were not effective at all under the same reaction conditions
(entries 4–8).
Scheme 1
Table 3 Substrate screening for Sn(0.77)/TN-catalysed Baeyer–Villiger oxidationa
Entry
Substrate
Time (h)
Product
Conv. (%)b
Yield (%)b
1
2
2
2
100
99
97
>99 (89)
98
2c
3d
97
4
5
6
10
100
>99 (78)
6
98
98 (93)
6
98
>99 (81)
7
6
77
72
a Substrate (0.5 mmol), Sn(0.77)/TN catalyst (0.05 g, Sn: 7.7 mol%), 1,2-DCE (1.5 mL), 30 wt% H2O2 (2 eq. relative to the ketone), reflux.
b Determined by GC using an internal standard technique. Values in parentheses were isolated yields. c 1st recycle. d 2nd recycle.
774 | Green Chem., 2012, 14, 771–777
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 4 Baeyer–Villiger oxidation with various TN-intercalated Sn
catalysta
Entry
Catalyst
CS (nm)b
Conv. (%)c
Yield (%)c
1
2
3
4
5
6
7
8
Sn(0.77)/TN
Sn(0.40)/TN
Sn(0.19)/TN
SnCl4·5H2O
SnCl2·2H2O
Sn(OH)4
0.55
0.52
0.27
—
—
—
79
90
75
85
100
trace
trace
trace
trace
trace
>99
n.d.d
n.d.d
n.d.d
n.d.d
n.d.d
SnO2
SnO
—
—
a Cyclopentanone (0.7 mmol), Sn catalyst (Sn: 0.77 mol% of substrate),
1,2-DCE (1.5 mL), 30 wt% H2O2 (2 eq. relative to ketone), reflux,
24 h.b Calculated from XRD profiles. c Determined by GC using an
internal standard technique. d Not detected.
Fig. 6 FT of Sn K-edge EXAFS spectra for (a) Sn(0.77)/TN, (b)
Sn(0.44)/TN, and (c) Sn(0.19)/TN catalyst. The solid curves are recov-
ered catalysts, and the dashed curves are fresh catalysts.
(4−x)+
that the highly dispersed monomeric [SnIV(OH)x(H2O)5−x
]
(x = 0–3) species in the TN interlayer can act as an effective
active species for this reaction.
Scheme 2
Conclusions
In the case of cyclopentanone as a substrate, the Sn(0.19)/TN
catalyst showed a high turnover number (TON; moles of product
per mole of Sn content) of 250, as demonstrated in Scheme 2.
This TON value of the Sn(0.19)/TN catalyst is the highest
reported for a Sn-containing heterogeneous catalyst system to
date. Other TON values include the following: 48 for Sn-β-zeoli-
te,5a 63 for Sn/hydrotalcite,6e 132 for Sn/palygorskite,6f 58 for
Sn/polystyrene,6d 9 for Sn-dendrimer/polystyrene,6a 4 for Sn-
dendrimer/cellulose,6c and 75 for Sn/montmorillonite.6g Further-
more, the highest TON value to date, 295, was also obtained in
the 2-adamantanone oxidation in the presence of the Sn(0.19)/
TN catalyst; other TON values include the following: 145 for
Sn-β-zeolite,5a 173 for Sn-MCM-41,6b 164 for Sn/palygorskite,6f
Isolated [SnIV(OH)x(H2O)5−x
]
(x = 0–3) species were able
(4−x)+
7
to intercalate into the TN interlayers, as confirmed by XRD, Li
MAS NMR, 119Sn MAS NMR, and Sn K-edge XAFS analyses.
Sn(0.19)/TN is an effective heterogeneous catalyst for the
Baeyer–Villiger oxidation of various cyclic ketones with excel-
lent TON values. No Sn leaching was observed during the oxi-
dations, and the catalyst was recyclable. We expect that our
intercalation protocol based on TN as a cation-exchanger will
offer an attractive route for the design of functional catalysts at
the atomic and molecular levels.
215 for Sn/polystyrene,6d 28 for Sn-dendrimer/polystyrene,6a
4
Experimental section
for Sn-dendrimer/cellulose,6c and 166 for Sn/montmorillonite.6g
After the reaction, the XRD profiles of the recovered TN-sup-
ported Sn catalysts revealed that the recovered catalyst had
almost the same layered structure as the fresh catalyst.9 The FT
of the k3-weighted Sn K-edge EXAFS data for the recovered
TN-intercalated Sn catalysts is shown in Fig. 6.22 In the second
coordination sphere of recovered Sn(0.77)/TN and recovered
Sn(0.40)/TN, however, the peak at approximately 0.35 nm corre-
sponding to the Sn–(O)–Sn bond was detected because of the
formation of an aggregated species such as SnO2 (Fig. 6a and
6b). In contrast, the SnIV species in the Sn(0.19)/TN interlayer
maintained its monomeric structure even after the oxidation reac-
tion (Fig. 6c). Based on the above results, it can be concluded
General
All organic chemical compounds were purified by standard pro-
cedures before use. Analytical GLC was performed by a Shi-
madzu GC-8A with a flame ionization detector equipped with
Thermon 3000 and Silicone OV-101 packing. GC-MS was per-
formed by a Shimadzu GC-17B with a thermal conductivity
detector equipped with an RT-βDEXsm capillary column. 1H
and 13C NMR spectra were obtained on JNM-AL400 or spec-
trometers at 400 MHz in chloroform-d1 with TMS as an internal
standard. Products were confirmed by the comparison of their
GC retention time, mass, 1H and 13C NMR spectra with those of
authentic samples. Data of XRD measurement were recorded on
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 771–777 | 775

View Article Online
a MAC Science MXP3V in reflection mode at 25 kV and 10 mA
using Cu-Kα radiation (α1 = 0.154057 nm, α2 = 0.154433 nm,
weighted average = 0.154178 nm). The samples were loaded on
glass plate sample holders whose reflections did not interfere
with their characterization. Infrared spectra were obtained with a
HORIBA FT-720. Samples were diluted with KBr and com-
pressed into thin disk shaped pellets. Spectra were taken in trans-
mission mode over the range of 400–4000 cm−1, with 16 scans
at 4 cm−1 resolutions. ICP measurements were performed on
SPS 1800H Plasma Spectrometer by SII (Sn element:
procedure. The obtained TN-intercalated Sn catalyst were abbre-
viated as (0.40)/TN and Sn(0.19)/TN, respectively.
Typical procedure for Baeyer–Villiger oxidation
Into a Schlenk tube with a reflux condenser was placed cyclo-
pentanone (0.5 mmol), Sn catalyt (Sn: 7.7 mol%), 1,2-dichlor-
oethane (1.5 mL), and 30 wt% H2O2 (2 eq. relative to ketone).
The resulting mixture was refluxed for 24 h. Cyclopentanone
conversion and lactone yields were periodically determined by
GC analysis. After 24 h, the Sn(0.77)/TN catalyst was separated
by a filtration. The filtrate was treated with MnO2, followed by
extraction with diethyl ether. The solvent was removed in vacuo,
and the residue was purified via bulb-to-bulb distillation or sili-
cagel column chromatography. Analytically pure δ-valerolactone
(0.0445 g, 89%) was obtained.
7
189.898 nm). The Li nuclear magnetic resonance spectra were
acquired using a superconducting magnet (600 MHz, JEOL
ECA-600). The sample rotor of zirconia (4.0 mm) was spun at
the spinning frequency of 15 kHz. The measurement of NMR
spectra was performed using the non-decoupling single-pulse
method. Chemical shifts were referenced to 1.0 mol L−1 of
aqueous LiCl as an external standard (0 ppm). The 119Sn nuclear
magnetic resonance spectra were acquired using a superconduct-
ing magnet (223.81 MHz, JEOL ECA-600). The sample rotor of
zirconia (3.2 mm) was spun at the spinning frequency of 20
kHz. The measurement of NMR spectra was performed using
the non-decoupling single-pulse method. Chemical shifts were
references to (CH3)4Sn as an external standard (0 ppm). X-ray
absorption spectra around the Sn K-edges were recorded at the
BL01B1 beamline of the SPring-8 (8 GeV, 100 mA) of the
Japan Synchrotron Radiation Research Institute (Proposal No.
2010B1100 by Professor Dr Kiyotomi Kaneda, Graduate School
of Engineering Science, Osaka University). A Si (311) two-
crystal monochromator was used. Ion chambers filled with
Ar(100%) and Ar(50%)/Kr(50%) were used for the I0 and I
detectors, respectively, and the samples were located between
these ion chambers. Energy calibration was carried out using a
Sn foil (30 mm of thickness). Sn K-edge XANES and EXAFS
spectra of all samples were recorded in the step scan mode. Data
reduction using the REX2000 Ver.2.3.3 program (Rigaku) was
carried out. The EXAFS analysis was performed as described
below. The spectra were extracted by utilizing the cubic spline
method and normalized to the edge height. The k3-weighted
EXAFS oscillation was Fourier transformed into r space, with
the Fourier transformation range between 3.0 and 16.0 Å−1. The
amount of hydrogen peroxide was determined by titration
method by use of KMnO4.
Acknowledgements
This study was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science, and Technology of Japan (19560771). Some of the
experiments were carried out at the BL01B1 beamline of the
SPring-8 of the Japan Synchrotron Radiation Research Institute
(Proposal No. 2010B1100)
References
1 A. Baeyer and V. Villiger, Ber. Dtsch. Chem. Ges., 1899, 32, 3625.
2 G. R. Krow, Org. React., 1993, 43, 251.
3 For review, see (a) M. Renz and B. Meunier, Eur. J. Org. Chem., 1999,
737; (b) G. Strukul, Angew. Chem., Int. Ed., 1998, 37, 1198; (c) G.-J. ten
Brink, I. W. C. E. Arends and R. A. Sheldon, Chem. Rev., 2004, 104,
4105.
4 C. Jiménez-Sanchidrián and J. R. Ruiz, Tetrahedron, 2008, 64, 2011.
5 (a) A. Corma, L. T. Nemeth, M. Renz and S. Valencia, Nature, 2001,
412, 423; (b) M. Renz, T. Blasco, A. Corma, V. Fornés, R. Jensen and
L. T. Nemeth, Chem.–Eur. J., 2002, 8, 4708; (c) S. R. Bare, S. D. Kelly,
W. Sinkler, J. J. Low, F. S. Modica, S. Valencia, A. Corma and
L. T. Nemeth, J. Am. Chem. Soc., 2005, 127, 12924; (d) M. Boronat,
A. Corma, M. Renz, G. Sastre and P. M. Viruela, Chem.–Eur. J., 2005,
11, 6905; (e) M. Boronat, P. Concepción, A. Corma and M. Renz, Catal.
Today, 2007, 121, 39.
6 (a) Q.-G. Zhang, S.-X. Wen and Z.-Q. Lei, React. Funct. Polym., 2006,
66, 1278; (b) A. Corma, M. T. Navarro, L. T. Nemeth and M. Renz,
Chem. Commun., 2001, 2190; (c) C.-L. Li, J.-Q. Wang, Z.-W. Yang,
Z.-G. Hu and Z.-Q. Lei, Catal. Commun., 2007, 8, 1202; (d) J.-Q. Wang,
R.-R. Wang, Z. Zhang, C.-L. Li, Z.-W. Yang and Z.-Q. Lei, J. Macromol.
Sci., Part A: Pure Appl. Chem., 2008, 45, 672; (e) U. R. Pillai and
E. Sahle-Demessie, J. Mol. Catal. A: Chem., 2003, 191, 93;
(f) Z.-Q. Lei, Q.-H. Zhang, J.-J. Luo and X.-Y. He, Tetrahedron Lett.,
2005, 46, 3505; (g) Z.-Q. Lei, G.-F. Ma and C.-G. Jia, Catal. Commun.,
2007, 8, 305; (h) A. Corma, M. T. Navarro and M. Renz, J. Catal., 2003,
219, 242; (i) M. Boronat, P. Concepción, A. Corma, M. T. Navarro,
M. Renz and S. Valencia, Phys. Chem. Chem. Phys., 2009, 11, 2876.
7 H. Toraya, S. Iwai, F. Marumo and H. Hirao, Z. Kristallogr., 1977, 146,
73.
8 (a) T. Sento, S. Shimazu, N. Ichikuni and T. Uematsu, Chem. Lett., 1998,
27, 1191; (b) S. Shimazu, M. Suzuki, N. Ichikuni and T. Uematsu, J. Ion
Exchange, 2003, 14, 397; (c) N. Yamaguchi, S. Shimazu, N. Ichikuni and
T. Uematsu, Chem. Lett., 2004, 33, 208; (d) Y. Permana, S. Shimazu,
N. Ichikuni and T. Uematsu, J. Mol. Catal. A: Chem., 2004, 221, 141;
(e) S. Shimazu, H. Zou, T. Hara and N. Ichikuni, J. Ion Exchange, 2007,
18, 584.
Preparation of TN-intercalated Sn catalysts
The intercalation of Sn species into TN interlayer was achieved
by the following procedure. Into a round-bottomed flask with Li/
TN (1 g), deionized water (10 mL) and methanol (10 mL) were
added, and then the mixture was stirred to swell at room temp-
erature. After 1 h, SnCl2·2H2O (0.15 g: 50% of CEC) in metha-
nol (30 mL) was added, followed by the addition of deionized
water (30 mL), and stirred at 30 °C for 48 h. The obtained slurry
was filtered, washed with deionized water, and dried under
vacuum overnight. The same intercalation procedure by use of
the above Sn-containing TN, was repeated two times, TN-inter-
calated Sn catalyst, Sn(0.77)/TN, was obtained. To control the
loading amount of Sn species, the Sn amount was changed to
0.08 g × 2 times or 0.038 g × 2 times in the intercalation
9 Data are shown in ESI†.
776 | Green Chem., 2012, 14, 771–777
This journal is © The Royal Society of Chemistry 2012

View Article Online
10 R. K. Harris, B. E. Mann, NMR and the Periodic Table, Academic Press,
amplitude functions were extracted from SnO2, which has a rutile tetra-
gonal lattice P42/mnm.
London, 1978.
11 P. Porion, A. M. Faugère and A. Delville, J. Phys. Chem. C, 2008, 112,
18 Since it is hard to discriminate between Sn–OH or Sn–(OH2) bond from
Sn K-edge XAFS analysis, the each coordination number of Sn–OH or
Sn–(OH2) bond can not be provided.
19 M. Intissar, J.-C. Jumas, J.-P. Besse and F. Leroux, Chem. Mater., 2003,
15, 4625.
20 Following the screening of solvent for Baeyer–Villiger oxidation, the
highest catalytic activity was obtained in 1,2-dichloroethane solvent,
shown in ESI†.
21 After the third and forth recycling experiment of Sn(0.77)/TN catalysed
Baeyer–Villiger oxidation, the yields of δ-valerolactone were 92% and
88%, respectively.
9808.
12 The same results are obtained in the characterisation of Na/TN, K TN−1
,
and Ca/TN by use of 7Li MAS NMR, as also shown in ESI†.
13 P. J. Smith and A. P. Tupciauskas, Annu. Rep. NMR Spectrosc., 1978, 8,
291.
14 Multinuclear Solid-State NMR of Inorganic Materials, Pergamon Materials
Series, ed. K. J. D. MacKenzie, Pergamon, Amsterdam, 2002, vol. 6.
15 B. Wrackmeyer, Annu. Rep. NMR Spectrosc., 1995, 16, 73.
16 C. Cossement, J. Darville, J.-M. Gilles, J. B. Nagy, C. Fernandez and
J.-P. Amoureux, Magn. Reson. Chem., 1992, 30, 263.
17 Curve-fitting analysis was performed for the Sn–O shell with the range of
the Sn–O shell being between 0.092 and 0.196 nm. The Sn–O phase and
22 Sn K-edge XANES spectra of the recovered catalysts are also shown in
the ESI†.
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 771–777 | 777