Selective Oxidation of Thioanisole with Hydrogen Peroxide using

Feb 15, 2018 - Department of Energy and Material Sciences, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan ... Fro...
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Selective Oxidation of Thioanisole with Hydrogen Peroxide using Copper Complexes Encapsulated in Zeolite; Formation of a Thermally Stable and Reactive Copper Hydroperoxo Species Syuhei Yamaguchi, Akinori Suzuki, Makoto Togawa, Maiko Nishibori, and Hidenori Yahiro ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b04092 • Publication Date (Web): 15 Feb 2018 Downloaded from http://pubs.acs.org on February 15, 2018

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ACS Catalysis

Selective Oxidation of Thioanisole with Hydrogen Peroxide using Copper Complexes Encapsulated in Zeolite; Formation of a Thermally Stable and Reactive Copper Hydroperoxo Species. Syuhei Yamaguchi,a Akinori Suzuki,a Makoto Togawa,a Maiko Nishibori,b and Hidenori Yahiro a* a

Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan.

b

Department of Energy and Material Sciences, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan.

KEYWORDS: Cu complex, Zeolite, Oxidation, Hydrogen peroxide, Thioanisole.

ABSTRACT: [Cu(terpy)]2+ complexes encapsulated into Na-Y zeolite ([Cu(terpy)]2+@Y) were prepared and their catalytic activity for the oxidation of sulfides using hydrogen peroxide were investigated. Several spectroscopic results, as well as elemental analysis, demonstrated the formation of [Cu(terpy)]2+ complexes in supercages of Y-zeolite. [Cu(terpy)]2+@Y exhibited high selectivity for the oxidation of thioanisole into methylphenylsulfoxide when using H2O2. The kinetic study for this oxidation at the catalyst [Cu(terpy)]2+@Y suggests that the reaction of [Cu(terpy)]2+ species with H2O2 is the rate determining step. The oxidation of thioanisole, benzene and 2-phenylethylamine using [[Cu(terpy)]2+@Y]*, which was prepared from the reaction between [Cu(terpy)]2+@Y and H2O2, quantitatively proceeded to methylphenylsulfoxide, phenol and 2-amino-1-phenylethanol, respectively. The reaction of [Cu(terpy)]2+@Y and H2O2 was found to yield thermally stable but active CuII-OOH species in [Cu(terpy)]2+@Y.

INTRODUCTION

whereas an active species is too unstable to be studied thoroughly.2-4

From a synthetic chemistry and biological point of view, mononuclear copper-hydroperoxo species have been considered as important active species for the partial oxidation of organic substrates when using hydrogen peroxide.1,2 Although a few well-characterized CuII-OOH complexes have been described,2,3 not a great deal is known about their intrinsic reactivity and reaction mechanism. Masuda et al.2,4 reported the catalytic activity of a CuII-OOH species for the selective oxidation of thioanisole to methylphenylsulfoxide. They demonstrated that the thermal stability of the species could be controlled by molecular design of the coordination geometry around the copper ion, and that the complex with a square-planar geometry exhibited the best performance among the tested complexes. Karlin et al.5 reported that a CuII-OOH species can perform oxidative N-dealkylation reactions on a pyridyl ligand with pendant dimethylamine and dibenzylamine moieties as substrate, resulting in the corresponding secondary amine and aldehyde (formaldehyde and benzaldehyde), derived from the oxidized methyl and benzyl groups. However, there is little information regarding the thermally stable but active CuII-OOH species because normally no substrate reacts with a thermally stable isolated CuII-OOH species,

From the standpoint of environmental issues, the development of green chemistry procedures and environmentally friendly technologies are crucial to achieve a sustainable growth. The immobilization of transition metal complexes in zeolite has attracted much interest for the development of catalysts that combine the advantages of homogeneous and heterogeneous catalysis.6-11 We previously reported that iron-bipyridine complexes encapsulated into Na-Y zeolite ([Fe(bpy)3]2+@Y) possess high catalytic activity for the oxidation of cyclohexene and benzene using hydrogen peroxide to form their corresponding alcohols with high selectivity.7 Furthermore, the maximum value of catalytic activity for the oxidation of benzene with H2O2 was achieved when the volume ratio of solvents (CH3CN and H2O) was equal (1:1).7c To this date, many have reported the immobilization of copper complexes in zeolite and their catalytic activity for the oxidation of sulfides,8 benzenes,9 alcohols,10 and other substrates11 using H2O2. However, little is known about their reactivity and reaction mechanism. The design concept of copper-terpyridine complexes encapsulated in Y-type zeolite ([Cu(terpy)]2+@Y) is shown

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in Scheme S1 (terpy = 2,2’:6',2''-terpyridine). Based on the report by Masuda et al. 2,4, it is expected that this complex, which has a square-planar geometry, would be active for the oxidation of organic substrates in presence of H2O2. In this study, we report the synthesis of the [Cu(terpy)]2+@Y catalyst and its characterization using different methods. Also, its catalytic activity on the oxidation of thioanisole with H2O2 was studied. Furthermore, the preparation and characterization of an activated catalyst were also investigated. This catalyst, [[Cu(terpy)]2+@Y]*, was obtained after the reaction of [Cu(terpy)]2+@Y with H2O2; its activity on the oxidation of thioanisole, benzene, 2phenylethylamine was evaluated.

filtration, then washed with water and methanol using a Soxhlet extractor, and finally dried at room temperature under vacuum to give [Cu(terpy)]2+@Y as a light-blue powder. Elemental analysis: C, 5.67; H, 2.22; N, 1.39; Na, 5.29; Cu, 2.13; and Al, 8.37 wt%. Preparation of [Cu(terpy)(CH3CN)](ClO4)2. This complex was synthesized for comparison with [Cu(terpy)]2+@Y. 2,2’:6',2''-terpyridine (0.10 g, 0.4 mmol) was added into a methanol solution (40 mL) of Cu(ClO4)2 ∙ 6H2O (0.158 g, 0.4 mmol) and stirred at room temperature for 1 h. After evaporation of the methanol, a blue powder was formed. Then, the precipitate was recrystallized from CH3CN/diethylether to yield needlelike blue crystals. Elemental analysis: C16H14Cl2CuN4O8∙ 0.25H2O (541.27) calcd. C 37.72, H 2.70, N 10.35; found C 37.63, H 2.61, N 10.17.

EXPERIMENTAL SECTION General. Na ion-exchanged Y-type zeolite (Na-Y) with SiO2/Al2O3 = 5.5 was acquired from Tosoh Co. All the materials used were of analytical grade, commercially available from Aldrich, Wako, and TCI.

Catalytic oxidation of thioanisole. The catalytic oxidation was evaluated in a glass tube reactor at 50 °C under air. The typical procedure was as follows: catalyst (17 µmol), MeCN solvent (10 mL), thioanisole (8.5 mmol), and 30% aqueous hydrogen peroxide (0.42 mmol) were placed into the tube. After the reaction, triphenylphosphine was added as a quencher and odichlorobenzene as an internal standard into the reactor. The reaction solution was analyzed via GC with a flame ionization detector (FID). The products were identified by comparison to authentic samples. The turnover number (TON) was calculated as the ratio of product per copper (TON [‒] = Product [mol]/Cu [mol]).

Instrumentation. The powder X-ray diffraction (XRD) patterns of the catalysts were collected on a Rigaku MiniFlex II diffractometer using CuKα radiation. UV–vis spectra were recorded on a Hitachi U-4000 spectrometer for solid samples or a Shimadzu U-1200 for liquid samples. The ESR measurements were performed at room temperature with a JEOL JES-FA200S X-band spectrometer. Before the ESR measurements, the sample was evacuated at room temperature. The ESR spectral line-shape simulation was carried out using the SimFonia software (Bruker). The FT-IR spectra of the samples with KBr powder were recorded using a PerkinElmer Spectrum One spectrometer. The specific surface area was determined via the BET analysis (Belsorp-mini, BEL Japan) for the adsorption-desorption measurements using N2 as adsorbent at −196 °C. Gas chromatograph (GC) analysis was performed on a Shimadzu GC-14B with a flame ionization detector equipped with a DB-1MS capillary column (internal diameter = 0.25 mm, length = 30 m) using a polar liquid phase. The X-ray absorption spectroscopy (XAS) spectra, including X-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) of Cu K-edge, were measured at room temperature in the transmission mode at the Kyushu University Beamline (BL06) in the Kyushu Synchrotron Light Research Center (SAGA-LS), Tosu, Japan. An appropriate amount of the samples and 80 mg of boron nitride powder were mixed and pressed into pellets a 10-mm diameter. Synchrotron radiation was monochromated by a Si (111) double crystal; a cylindrical mirror coated with rhodium was used to eliminate higher harmonics. The data were analyzed using ATHENA and ARTEMIS, a suite of IFEFFIT software programs.12

Pretreatment of catalysts with H2O2 ([[Cu(terpy)]2+@Y]* and [Cu-Y]*). When [Cu(terpy)]2+@Y (0.050 g, 17 µmol) reacted with 30% aqueous hydrogen peroxide (0.42 mmol) in acetonitrile (10 mL) for 3 h at room temperature, the color of the catalyst in the suspension changed from light-blue to light-green. The light-green powder, [[Cu(terpy)]2+@Y]*, was filtrated and then washed and centrifuged three times with acetonitrile to remove unreacted hydrogen peroxide (Scheme S2). The same method was used for the light-blue Cu-Y powder; however, the color remained the same for the activated [Cu-Y]*. The partial oxidation of thioanisole without hydrogen peroxide was performed at 50 °C under air as a reference reaction to evaluate the catalytic activity of [[Cu(terpy)]2+@Y]* and [Cu-Y]*. The typical conditions were: catalyst (17.0 µmol Cu atoms in catalysts), thioanisole (8.5 mmol), and acetonitrile (10 mL). RESULTS AND DISCUSSION Characterization of [Cu(terpy)]2+@Y. The estimated molecular diameter of [Cu(terpy)]2+ is 8.1–9.8 Å.13 The Ytype zeolite, which belongs to the faujasite family, has cavities with a diameter of ca. 13.0 Å, the so-called supercages.14 These supercages are connected to each other by tunnels or windows with a diameter of maximum ca. 7.4 Å.14 The estimated diameter of the complex is larger than the window size but smaller than the supercage, thus it can be synthesized inside the supercage.

Preparation of the [Cu(terpy)]2+@Y catalyst. Na-Y zeolite (5.0 g) was ion-exchanged via a conventional method using an aqueous solution (300 mL) of Cu(NO3)2∙ 3H2O (0.36 g, 1.5 mmol) to yield copper(II) ion-exchanged Y-type zeolite (Cu-Y). The obtained Cu-Y (1.0 g) was refluxed in a methanol solution (100 mL) of 2,2’:6',2''terpyridine (0.0734 g, 1.6 mmol) for 20 h, followed by

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ACS Catalysis ICP-AES and elemental analysis of [Cu(terpy)]2+@Y were carried out after the sample was dissolved in a HF solution (Table S1). The [Cu(terpy)]2+@Y sample contained 2.1 wt% copper(II) ions, 5.7 wt% C atoms, and 1.4 wt% N. This indicates that the terpy/Cu ratio is ca. 1.0, suggesting that the Cu ion in zeolite Y was coordinated with one terpy ligand to yield the [Cu(terpy)]2+ ion. BET surface area of [Cu(terpy)]2+@Y (579 m2g−1) remarkably decreased as compared to that of Cu-Y (796 m2g−1). In the TG/DTA results (Fig. S1), the exothermic peaks derived from the combustion of terpy ligands in the complex were observed around 350 °C for [Cu(terpy)(CH3CN)](ClO4)2 + Na-Y and 500 °C for [Cu(terpy)]2+@Y. The thermal stability of the ligand in the latter was higher than in the former because the zeolite framework protected terpy from heat. BET and TG/DTA results suggest that complex ions were located within the zeolite cages.

2+

Figure 1. XRD patterns of (a) [Cu(terpy)] @Y, (b) Cu-Y, and (c) Na-Y.

2+

The IR spectra of [Cu(terpy)] @Y, Cu-Y, Na-Y, and [Cu(terpy)(CH3CN)](ClO4)2 were recorded (Fig. S2). The perchlorate complex showed sharp bands in the range of 1200–1600 cm−1, Fig. S2(d), which can be assigned to the ν(C−N) and ν(C−C) of the pyridine ring in terpy.15 Similar ν(C−N) bands were observed for [Cu(terpy)]2+@Y, Fig. S2(a). For this complex, the IR peaks corresponding to [Cu(terpy)]2+ were observed even after Soxhlet extraction, suggesting that these ions were present in the supercage of zeolite Y. The presence of free terpy embedded in Cu-Y was ruled out because uncoordinated terpy that has a kinetic diameter smaller than the pore opening of zeolite Y would be easily removed during Soxhlet extraction. IR spectra of [Cu(terpy)]2+@Y, Cu-Y, and Na-Y showed intense bands in the ranges of 1000–1200 cm−1 and 700– 800 cm−1 respectively assigned to the νas(OTO) and νs(OTO) bands, which are derived from the zeolite framework.

The UV–vis diffuse reflectance spectra of [Cu(terpy)]2+@Y, Cu-Y, and Na-Y are shown in Fig. 2. No absorption was observed from the ultraviolet to visible region in the absence of metal complexes. The spectrum of [Cu(terpy)]2+@Y presented two absorption bands at 680 and 336 nm, which can be assigned to a d-d and a ππ* transition of the terpy ligand. Similar bands were observed for [Cu(terpy)(CH3CN)](ClO4)2 + Na-Y (Fig. S3(b)) and [Cu(terpy)(CH3CN)](ClO4)2 (Fig. S4(a)) in CH3OH. Despite having the same concentration of [Cu(terpy)]2+, the intensity of the π-π* band in [Cu(terpy)]2+@Y was larger than in [Cu(terpy)(CH3CN)](ClO4)2 + Na-Y (Fig. S3). For the [Cu(terpy)(OH2)](CF3SO3)2 single crystal reported by Castro et al.,12 the terpy ligands of [Cu(terpy)]2+ are close to each other due to π-π stacking between the pyridine rings of the ligands. The intermolecular π-π stacking interaction of terpy in [Cu(terpy)]2+@Y was inhibited by immobilization of the complex into the supercage, resulting in the increased intensity of the band assigned to the π-π* transition.

The XRD patterns of [Cu(terpy)]2+@Y, Cu-Y, and Na-Y are shown in Fig. 1. This figure demonstrates that the zeolite Y structure remained after the introduction of the metal-complex. It has been reported that the empirically derived relationship between the relative peak intensities of the (220) and (311) reflections, represented by I220 and I311, in the XRD pattern confirms the formation of a large metal complex ion in the supercage of faujasite-type zeolites: I220 > I311 for the original zeolite Y and I220 < I311 for the zeolite containing large complexes.7 As can be seen in Fig. 1, I220 (2θ = 10°) was greater than I311 (2θ = 12°) for Cu-Y, and Na-Y (Figs. 1(b) and 1(c)), the opposite was observed for [Cu(terpy)]2+@Y (Fig. 1(a)). This is one of evidences of the formation of copper-complex ions within the supercage.

Figure 2. UV–vis diffuse reflectance spectra of (a) 2+ [Cu(terpy)] @Y, (b) Cu-Y, and (c) Na-Y.

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The ESR spectra of the [Cu(terpy)]2+@Y and Cu-Y samples evacuated at 150 °C for 2 h are shown in Fig. 3. The characteristic ESR signals of isolated Cu2+ ion (I=3/2) were observed for [Cu(terpy)]2+@Y and Cu-Y; however, the determined ESR parameters of [Cu(terpy)]2+@Y (g// = 2.24, g⊥ = 2.05, and |A//| = 171 G) were clearly different from those of Cu-Y (g// = 2.40, g⊥ = 2.06, and |A//| = 123 G). The hyperfine splitting constant of [Cu(terpy)]2+@Y was larger than that of Cu-Y. In addition, the ESR parameters of [Cu(terpy)]2+@Y and Cu-Y were respectively similar to those of [Cu(terpy)(CH3CN)](ClO4)2 (g// = 2.27, g⊥ = 2.05, |A//| = 163 G) and [Cu(OH2)6](ClO4)2 (g// = 2.43, g⊥ = 2.08, |A//| = 108 G) in CH3CN at 77 K (Fig. S5(a)).

not corrected in this study. A strong peak at around 1.5 Å corresponds to a Cu-N bond. Table S2 indicates the results of EXAFS curve fittings of [Cu(terpy)]2+@Y and [Cu(terpy)(CH3CN)](ClO4)2. The Cu-N interatomic distance of [Cu(terpy)]2+@Y (1.97 Å) was equivalent to that of [Cu(terpy)(CH3CN)](ClO4)2 (1.98 Å). All the results suggest that [Cu(terpy)]2+ complex ions with a square-planar geometry could be formed in the supercages of Y-type zeolite.

These results led us to the conclusion that the coordination environment around copper in Cu-Y was changed from a six-coordinated distorted octahedral geometry to a four-coordinated square-planar one after the introduction of terpy.16 The present ESR spectra gave no information of the kind of ligands in the coordination sphere of Cu. It was reported that Cu ion introduced in Yzeolite is coordinated with 6 water molecules to give octahedral geometry at ambient atmosphere and that upon evacuation at high temperature, the octahedral geometry was distorted by the change in the ligand from the oxygen of water molecule to the lattice oxygen in zeolite framework.17 Combining above facts with the elemental analysis and TG-DTA result in this study, the Cu ion in [Cu(terpy)]2+@Y is probably coordinated with three N atoms in terpy and one O atom in water (or one O atom in zeolite framework).

Figure 4. (A) Cu K-edge XANES and (B) Fourier 3 2+ transformation of k -weighted EXAFS of (a) [Cu(terpy)] @Y, (b) [Cu(terpy)(CH3CN)](ClO4)2, (c) Cu-Y, and (d) Cu foil. F.T. range was fixed to 3-12 Å for both EXAFS spectra.

Catalytic activities for the oxidation of thioanisole. Masuda et al.2,4 investigated the thioanisole oxidation activity of Cu complexes with H2O2 as oxidant at a 10- or 100-fold thioanisole to H2O2. Such conditions, where the amount of substrate is much larger than that of oxidant, are generally used in the re-oxidation of sulphoxides to sulphones. Therefore, similar conditions were used in this report. Fig. 5 shows the time course for the oxidation of thioanisole with H2O2 over heterogeneous [Cu(terpy)]2+@Y and homogeneous [Cu(terpy)(CH3CN)](ClO4)2 catalysts under air. No catalytic activity was observed with Na-Y and without a catalyst under the same experimental conditions. For [Cu(terpy)]2+@Y and [Cu(terpy)(CH3CN)](ClO4)2, the amount of methylphenylsulfoxide increased with time, although the production of methylphenylsulfone by reoxidation of the sulfoxide was not observed. The reaction rate of [Cu(terpy)(CH3CN)](ClO4)2 was faster than that of [Cu(terpy)]2+@Y, though the catalytic activity of the latter was comparable to that of the former in steady state. It is worth noting that [Cu(terpy)]2+@Y was conveniently separated by filtration and reused under similar conditions. The [Cu(terpy)]2+@Y catalyst was used at least five times without significant loss of catalytic activity and selectivity (Figure S7 and Table S3).

Figure 3. ESR (X band, RT, solid) spectra of (a) Cu-Y and 2+ (b) [Cu(terpy)] @Y.

Fig. 4(A) shows the Cu K-edge XANES spectra of [Cu(terpy)]2+@Y together with the reference compounds [Cu(terpy)(CH3CN)](ClO4)2, Cu-Y and Cu foil. The spectrum of [Cu(terpy)]2+@Y was very similar to that of [Cu(terpy)(CH3CN)](ClO4)2, but was clearly different from those of Cu-Y and Cu foil. The edge position (measured at the half-height of the edge jump) of [Cu(terpy)]2+@Y (8988.5 eV) was almost the same as that of [Cu(terpy)(CH3CN)](ClO4)2 (8988.9 eV), indicating that Cu ions in both compounds have the same electronic states. Fig. 4(B) shows the Fourier transformation of k3weighted EXAFS oscillations (Fig. S6). The phase shift was

The kinetic study for the oxidation of thioanisole showed adequate zero-order plots for the amount of

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ACS Catalysis thioanisole (1.70−17.0 mol) consumed (Figure S8). In addition, the first-order dependence of the reaction rate on the amount of [Cu(terpy)]2+@Y catalyst (3.40−34.0 mol) (Figure S9) and on the amount of H2O2 (0.42−1.26 mol) (Figure S10) was observed. Therefore, the reaction rate can be expressed as v = ktotal[Cu][H2O2]. This suggests that the reaction of [Cu(terpy)]2+ species with H2O2 to form CuII-OOH species is the rate determining step (Scheme S3).

Figure 6. UV–vis diffuse reflectance spectra of 2+ 2+ [Cu(terpy)] @Y (solid line) and [[Cu(terpy)] @Y]* (dashed 2+ line). Inset: difference spectrum of [[Cu(terpy)] @Y]* and 2+ [Cu(terpy)] @Y.

When H2O2 was added to [Cu(terpy)]2+@Y and Cu-Y, the former changed from blue to green, whereas the latter exhibited no change. The [Cu(terpy)]2+@Y] obtained after the reaction with H2O2 ([[Cu(terpy)]2+@Y]*) was used for the oxidation of thioanisole (Figs. 7 and S12). For [[Cu(terpy)]2+@Y]*, the maximum value of turnover number respect to Cu (TON) reached the unity after 16 h. On the other hand, the [Cu-Y]* sample exhibited no catalytic activity at all (Fig. S11). The oxidation of benzene and 2-phenylethylamine over [[Cu(terpy)]2+@Y]* also quantitatively proceeded (Fig. 7) under the same conditions than for thioanisole; phenol and 2-amino-1phenylethanol were selectively obtained. It should be noted that the time to reach the maximum value (TON ~ 1) for oxidation of benzene (240 h) was much longer than for methylphenylsulfoxide (16 h) and 2-phenethylbenzene (48 h) (Fig. 7). This means that the activity of [[Cu(terpy)]2+@Y]* lasted for at least 240 h at 50 °C. These results indicate that active and thermal stable CuII-OOH species were generated in [Cu(terpy)]2+@Y].

Figure 5. Time courses for the oxidation of thioanisole with hydrogen peroxide to yield methylphenylsulfoxide over [Cu(terpy)]2+@Y (a) and [Cu(terpy)(CH3CN)](ClO4)2 (b). Reaction conditions: Cu in catalysts (17 µmol), thioanisole (8.5 mmol), 30% aqueous H2O2 (0.42 mmol), CH3CN (10 mL), 50 °C, air atmosphere. TON [‒] = Product [mol]/Cu[mol].

To further examine the formation of CuII-OOH species in this system, the reaction between [Cu(terpy)]2+@Y and H2O2 was investigated in detail. The UV–vis band due to LMCT from OOH‒ to Cu 2-5,18,19 was observed at ca. 380 nm for [[Cu(terpy)]2+@Y]* after the reaction of [Cu(terpy)]2+@Y and H2O2 (Fig. 6). The ESR parameters of [[Cu(terpy)]2+@Y]* (g// = 2.24, g⊥ = 2.06, |A//| = 180 G) indicated that the mononuclear CuII center maintained a square planar geometry (Fig. S11). These kinetic and spectroscopic results suggest that the mononuclear CuIIOOH species was probably generated in the zeolite. The observation of resonance Raman peaks assigned to O-O stretching vibration would provide evidence of the formation of CuII-OOH species. However, unfortunately, no resonance Raman peaks (laser excitation wavelength of 406.7 nm) was observed due to very strong Rayleigh scattering derived from the zeolite frames.

The reason why the catalytically active CuII-OOH species is thermally stable in zeolitic media is still unclear. However, a similar phenomenon has been reported: the “cage effects,” where the zeolitic media enhances the stability of unstable radical species. 20 For example, it was demonstrated that the radical cations, [(CH3)3N]+ and [(CH3)3NCH2] +, in a sodalite cage of SAPO-37, a β-cage of SAPO-42, and in the main channel of Al-offretite are stable even at room temperature.21 Onaka et al. reported the long-term storage of unstable monomeric formaldehyde in Na-X and Na-Y at ambient temperature.22

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experiments were performed at Kyushu University Beamline (SAGA-LS /BL06) with the proposal of No. 2012IK009. We are grateful to Dr. S. Yanagisawa and Prof. T. Ogura (University of Hyogo) for measurement of resonance Raman spectrum.

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2+

Figure 7. Reaction activity of [Cu(terpy)] @Y]* for the oxidation of thioanisole to methylphenylsulfoxide, phenyethylamine to 2-amino-1-phenylethanol, and benzene to phenol. Substrate (8.5 mmol), Cu (17.0 µmol), CH3CN (10 mL), 50 °C. TON [‒] = Product [mol]/Cu[mol].

CONCLUSION [Cu(terpy)]2+ complex ions with square-planar geometry were prepared within supercages of Na-Y. The sulfoxide selective oxidation of thioanisole using H2O2 proceeded at [Cu(terpy)]2+@Y. The recycling test of this catalyst demonstrated no degradation in neither the catalytic activity nor in the selectivity after at least five runs. From the kinetic study, the reaction rate can be expressed as v = ktotal[Cu][H2O2]. This suggests that the formation of CuOOH is the rate-determining step. For the oxidation of thioanisole, 2-phenethylamine, and phenol over [[Cu(terpy)]2+@Y]*, which was prepared by the reaction between [Cu(terpy)]2+@Y and H2O2, the maximum value of TON was ca. 1. It was found that active and stable CuOOH species were formed in [Cu(terpy)]2+@Y.

ASSOCIATED CONTENT Supporting Information Synthetic and analytical details, Figures S1-11 including TGDTA, IR, UV–vis, ESR, EXAFS spectra, catalytic reaction results, Tables S1-3, and Schemes S1-3. This material is available free of charge via the internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * [email protected]

ORCID Syuhei Yamaguchi: 0000-0002-6669-3597 Hidenori Yahiro: 0000-0002-0415-1725

ACKNOWLEDGMENT This work was supported by JSPS KAKENHI Grant Numbers JP25820394 and JP16K06855, and CREST, JST. The XAFS

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