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the quantitative analyses, a single-pulse nondecoupling sequence
was used to avoid any effects of incomplete decoupling. The spec-
tra were measured for 1000 scans with a 458 pulse (pulse width=
4.25 ms) and a pulse delay of 60 s. The accumulated flame ioniza-
tion detector was processed without window functions. Chemical
shifts (d) were reported in ppm downfield from 85% H3PO4.
NH4H2PO4 (1.00 ppm) was used as an external standard for the cali-
bration of chemical shifts. Inductively coupled plasma combined
with atomic emission spectroscopy analyses were performed with
a Shimadzu ICPS-8100 spectrometer. The BET surface areas were
measured on a Micromeritics ASAP 2010 analyzer and calculated
from the N2 adsorption isotherm by using the BET equation. GC
analyses were performed on Shimadzu GC-2014 gas chromato-
graph equipped with a flame ionization detector and a DB-WAX
capillary column (internal diameter: 0.25 mm; length: 30 m) or
a TC-1 capillary column (internal diameter: 0.25 mm; length: 30 m).
The cold-spray ionization mass (CSI MS) spectra were recorded on
a JEOL JMS-T100CS spectrometer. Typical measurement conditions
were as follows: orifice voltage 85 V for positive ions; sample flow
0.1 mLminÀ1; solvent CH3CN; concentration 0.1 mm; spray temper-
ature 263 K; ion source at RT.
Conclusions
We have developed efficient heterogeneous catalysts for H2O2-
based selective oxidation by the immobilization of phospho-
rus-containing tetranuclear peroxotungstate ([PO4{WO(O2)2}4]3À
,
denoted by PW4) onto the zinc-modified supports (PW4-Zn(x)/
SnO2). Most importantly, the catalytic performance of PW4-
Zn(0.8)/SnO2 was much higher than that of the corresponding
homogeneous analogue THA3PW4 (THA=tetra-n-hexylammo-
nium). In the presence of PW4-Zn(0.8)/SnO2, various types of
organic substrates such as alkenes, amines, silanes, and sulfides
could be converted into the corresponding epoxides, N-oxides,
silanols, and sulfoxides (or sulfones), respectively, in high to ex-
cellent yields. The observed catalysis for the present oxidation
was truly heterogeneous, and the recovered catalyst could be
reused without significant loss of its high catalytic per-
formance.
Experimental Section
Materials
Synthesis and characterization of THA3PW4
The THA salt of [PO4{WO(O2)2}4]3À (THA3PW4) was synthesized ac-
cording to the procedure described in the literature.[8b] Yield:
1.39 g (50%); 31P NMR (CD3CN, 298 K): d=4.5 ppm (2JW-P =18.5 Hz);
CH3CN (Kanto Chemical Co., Inc.) was purified with the Ultimate
Solvent System (Glass Contour Company) before use.[20] Substrates
were purified according to the reported procedures.[21] Deuterated
solvents (CD3CN, CDCl3, and D2O) were purchased from Acros Or-
ganics and used as received. Tungstic acid (Wako Pure Chemical In-
dustries, Ltd), H3PO4 (85% aqueous solution, Kanto Chemical),
tetra-n-hexylammonium chloride (Aldrich), H2O2 (30% aqueous so-
lution, Kanto Chemical), zinc nitrate hexahydrate (Kanto Chemical),
and solvents [DMC, EtOAc, CH2Cl2, and (C2H5)2O (Kanto Chemical)]
were purchased and used as received. A solution of 60% aqueous
H2O2 was prepared by concentrating 30% aqueous H2O2. SnO2
(Guaranteed Reagent, >98%, Kanto Chemical, BET surface area:
51 m2 gÀ1), SiO2 (CARiACT G-3CN, Fuji Silysia Chemical Ltd., BET sur-
face area: 335 m2 gÀ1), g-Al2O3 (NKHD-24, Sumitomo Chemical Co.,
Ltd., BET surface area: 300 m2 gÀ1), TiO2 (ST-01, Ishihara Sangyo
Kaisha, Ltd., BET surface area: 129 m2 gÀ1), ZrO2 (RC-100, Daiichi Ki-
genso Kagaku Kogyo Co., Ltd., BET surface area: 89 m2 gÀ1), and
ZnO (BET surface area: 27 m2 gÀ1) were used as supports. These
supports were pretreated by calcination in air at 673 K for 3 h.
183W NMR (CD3CN, 298 K): d=À588.2 ppm (2JW-P =18.4 Hz, Dv1/2
=
7.3 Hz); IR (KCl): n˜ =977, 853, 843, 797, 757, 728, 660, 649, 603, 591,
573, 549, 525, 444 cmÀ1; Raman: n˜ =990, 864, 821, 655, 597, 580,
543, 391, 333, 305, 266, 237 cmÀ1; UV/Vis (CH3CN) lmax (e)=
254.2 nm (1268 molÀW1 dm3 cmÀ1); positive ion MS (CSI, CH3CN): m/z:
2569 [(THA)4PO4{WO(O2)2}4]+; elemental analysis calcd (%) for
C72H156N3O24PW4 ((THA)3[PO4{WO(O2)2}4]): C 39.05, H 7.10, N 1.90, P
1.40, W 32.22; found: C 38.82, H 6.97, N 1.36, P 1.36, W 33.28.
Preparation of PW4-Zn(0.8)/SnO2
An aqueous solution (20 mL) of zinc nitrate hexahydrate (38.7 mg,
130 mmol) containing SnO2 (1.0 g) was stirred vigorously for 1 h at
RT. The solution was evaporated to dryness at 323 K, and the re-
sulting solid was calcined in air for 2 h at 473 K, which gave
Zn(0.8)/SnO2. Then, a CH3CN solution (10 mL) of THA3PW4 (188 mg,
85 mmol) and 60% aqueous H2O2 (30 mL, 680 mmol) containing
Zn(0.8)/SnO2 was stirred vigorously for 1 h at RT. The resulting solid
was collected through filtration, washed with cooled CH3CN
(400 mL), and evacuated to dryness at RT. The pale yellow solid of
PW4-Zn(0.8)/SnO2 was obtained. The contents of phosphorus and
tungsten were 0.065 and 1.85 wt%, respectively. The other sup-
ported PW4 catalysts were prepared by using the procedure de-
scribed above.
Instruments
The IR spectra were recorded on a JASCO FT/IR-4100 spectrometer
Plus using KCl disks. The Raman spectra were recorded on a JASCO
NRS 5100 spectrometer with excitation at 531.99 nm. The UV/Vis
spectra were recorded on a JASCO V-570 spectrometer. The solu-
tion-state NMR spectra were recorded on a JEOL JNM-EX270 spec-
trometer (1H NMR: 270.0 MHz; 13C NMR: 67.8 MHz; 31P NMR:
109.3 MHz; 183W NMR: 11.2 MHz) with 5 mm tubes (for 1H and
13C NMR) or 10 mm tubes (for 31P and 183W NMR) or on a JEOL ECA-
500 spectrometer (1H NMR: 495.1 MHz; 13C NMR: 124.5 MHz) with
5 mm tubes. Chemical shifts were reported as parts per million in
the d scale downfield from SiMe4 (solvent, CDCl3) for 1H and
13C NMR spectra, 85% H3PO4 for 31P NMR spectra, and 2m Na2WO4
(solvent, D2O) for 183W NMR spectra. The solid-state 31P MAS (MAS
rate=5 kHz) NMR spectra were recorded on a JEOL ECA-500 spec-
trometer at 200.4 MHz by using 8 mm zirconia rotor. The 908 pulse
width was 8.5 ms. The relaxation time for PW4-Zn(x)/SnO2 (t1 =
14.4 s) was calculated by using an inversion recovery method. For
Procedure for catalytic oxidation
The catalytic oxidation of organic substrates was performed in
a 30 mL glass vessel containing a magnetic stir bar. The epoxida-
tion of 1c was performed with an autoclave reactor with a Teflon
vessel. A typical procedure for catalytic oxidation was as follows:
1a (1 mmol), 60% aqueous H2O2 (1.2 mmol), and DMC (3 mL) were
charged to the reactor. The reaction was initiated by the addition
of PW4-Zn(0.8)/SnO2 (W 3.5 mol% with respect to 1a), and the re-
action solution was periodically analyzed by using GC. The remain-
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