Gold (III) phosphorus complex immobilized on fibrous nano-silica as a catalyst for the cyclization of propargylic amines with CO2

Accepted Manuscript Title: Gold (III) phosphorus complex immobilized on fibrous nano-silica as a catalyst for the cyclization of propargylic amines with CO2 Author: Seyed Mohsen PII: DOI: Reference:

S1381-1169(16)30251-5 http://dx.doi.org/doi:10.1016/j.molcata.2016.07.001 MOLCAA 9935

To appear in:

Journal of Molecular Catalysis A: Chemical

Received date: Revised date: Accepted date:

9-5-2016 30-6-2016 1-7-2016

Please cite this article as: Seyed Mohsen, Gold (III) phosphorus complex immobilized on fibrous nano-silica as a catalyst for the cyclization of propargylic amines with CO2, Journal of Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2016.07.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Gold (III) phosphorus complex immobilized on fibrous nanosilica as a catalyst for the cyclization of propargylic amines with CO2 Seyed Mohsen Sadeghzadeh

Department of Chemistry, College of Sciences, Sina Masihabadi Student Research, P.O. Box 97175-615, Neishabour, Iran. Fax/Tel: +98 561 2502065; E-mail: [email protected]

Graphical Abstract

Gold (III) phosphorus complex immobilized on fibrous nano-silica as a catalyst for the cyclization of propargylic amines with CO2

Highlights 1- HPG@KCC-1/PPh2/Au NP was synthesized for the first time. 2- It was used as a recyclable catalyst for the synthesis oxazolidinones. 3- In this method, catalyst separation was easily performable by filtration.

Abstract In this study, The HPG@KCC-1 NP was prepared through the ringopening polymerization of glycidol on the surface of KCC-1 to form HPG@KCC-1 and then HPG@KCC-1 NPs were functionalized using chlorodiphenylphosphine and phosphine-functionalized nanoparticles (HPG@KCC-1/PPh2) as a recyclable phosphorus ligand was obtained. Also, gold (III) complex of HPG@KCC-1/PPh2 ligand (HPG@KCC-1/PPh2/Au) was prepared which used for the cyclization of propargylic amines with CO2 to provide 2-oxazolidinones. High catalytic activity and ease of recovery from the reaction mixture using filtration, and several reuse times without significant losses in performance are additional eco-friendly attributes of this catalytic system.

Keywords: KCC-1, Nanocatalyst, One-pot synthesis, Green Chemistry, Fibrous nano-silica

Introduction Development of green processes based on chemical stabilization of carbon dioxide has received a great deal of interest in recent years because CO2 could be used as a safe, cheap, and renewable C1 building block to synthesize useful organic compounds. Various useful chemicals, such as dimethyl carbonate,[1] urethanes,[2] formic acid,[3] methanol,[4] cyclic carbonates,[5] polycarbonates,[6] and others have been prepared by using CO2 as a feedstock. One of the useful developments in which CO2 has been utilized as a substrate is through the carboxylative cyclization of propargylic amines with CO2 to provide 2-oxazolidinones.[7] 2Oxazolidinones are important heterocyclic chemicals playing a important role as chemical intermediates [8] and chiral auxiliaries [9] in organic synthesis, and as antibacterial drugs [10] in pharmaceutical chemistry. One of the most promising examples of CO2 fixation to access 2-oxazolidinones is the carboxylative cyclization of propargylic amines with CO2, which stands for an important clean and atom economic reaction. Gold catalysis has quickly become a hot topic in chemistry in the past decade.[11] Gold species are equally impressive as heterogeneous or homogeneous catalyst,[12,13] which showed excellent results in diversified reactions.[14,15] Gold complexes have been employed as a highly efficient catalyst for the formation of C-O, C-C, C-S, C-N, C-P, and C-F bonds starting from alkenes and alkynes.[16-18] From the viewpoint of the reactivity, Au complexes involving phosphorus ligands are one of the reactive classes of Au catalysts. Supporting these ligands on a recyclable support is one of the most important approaches to improve their applicability in organic reactions.[19] In recent years, it has been revealed that the use of gold complex grafted on the solid supports played an important role in preventing the aggregation of Au.[20] This superior performance of the HPG@KCC-1/PPh2/Au catalyst has been attributed to gold complex units incorporated into the fibers, which prevent the formation of agglomerated gold whilst maintaining the catalytic activity of gold species. Considering the importance of the chemical stabilization of carbon dioxide as well as remarkable properties of gold (III) complex based nanomaterials in organic transformations, we prepared novel phosphinefunctionalized ordered mesofibers organosilica (HPG@KCC-1/PPh2) material by using chlorodiphenylphosphine and tetramethoxysilane as silica precursors after that KCC-1 functionalized with glycidol to form HPG@KCC-1. The HPG@KCC-1/PPh2 material was then used as an efficient support for the immobilization of the gold (III) (HPG@KCC-

1/PPh2/Au) as catalysts for the synthesis 2-oxazolidinone. The recyclability, reusability and stability of the catalyst have also been investigated (Scheme 1).

Experimental General Procedure for the Preparation of KCC-1 and HPG@KCC-1 NPs The KCC-1 and HPG@KCC-1NPs core–shell microspheres were synthesized according to the previously reported method [21]. TEOS (2.5 g) was dissolved in a solution of cyclohexane (30 mL) and 1-pentanol (1.5 mL). A stirred solution of cetylpyridinium bromide (CPB 1 g) and urea (0.6 g) in water (30 mL) was then added. The resulting mixture was continually stirred for 45 min at room temperature and then placed in a teflon-sealed hydrothermal reactor and heated 120 °C for 5 h. The silica formed was isolated by centrifugation, washed with deionized water and acetone, and dried in a drying oven. This material was then calcined at 550 °C for 5 h in air. Then, For Synthesis of HPG@KCC-1 NPs, 2 mmol of KCC-1 NPs were dispersed in a mixture of 80 mL of toluene, and 1.0 mmol of potassium methylate (CH3OK), followed by the addition of 10 mL of anhydrous dioxane. 2.0 g of Glycidol was added dropwise over a period of 1 h. After vigorous stirring for 2 h, the final suspension was repeatedly washed, filtered for several times and dried at 60 °C in the air.

General procedure for the preparation of HPG@KCC-1/PPh2 NPs HPG@KCC-1 (0.6 g) was suspended in 60 mL of 0.1 M toluene solution of ClPPh2 and the colloidal solution was refluxed for 48 h. HPG@KCC-1/PPh2 NP was isolated and purified by repeated washing (first in ethanol and then in deionized water) and centrifugation.

General procedure for the preparation of HPG@KCC-1/PPh2/Au NPs Sodium tetrachloroaurate (III) hydrate (5 mmol) was dispersed in dry CH2Cl2 (20 ml) and HPG@KCC-1/PPh2 (0.1 g) nanoparticles were added. Then the mixture was heated to 60 °C for 12 h under nitrogen atmosphere. The resulting solid was separated by centrifugation and washed 3 times with CH2Cl2, ethanol and H2O. After drying at room temperature under vacuum, HPG@KCC-1/PPh2/Au NPs were obtained as powder.

General procedure for preparation of 2-oxazolidinones To a Schlenk-tube were successively added HPG@KCC-1/PPh2/Au NPs (0.1 mg), degassed water (1 mL) and a propargylic amine (1 mmol) under an argon atmosphere, and the inside of the Schlenk-tube was replaced with CO2 (0.5 MPa). The carboxylative cyclization of the propargylic amine with CO2 proceeded by the stirring of the resulting mixture at room temperature. Upon completion, the progress of the reaction was monitored by TLC when the reaction was completed, methanol and dichloromethane were added to the reaction mixture and the catalyst was separated by filtration under vacuum. Then the solvent was removed from solution under reduced pressure and the resulting product purified by recrystallization using methanol.

Spectral data of synthesized compounds: 3-butyl-5-methyleneoxazolidin-2-one (Compound 2a):[22] Yellow oil; 1H NMR (400 MHz; CDCl3) δ = 0.90 (t, J = 7.2 Hz, 3H), 1.31-1.22 (m, 2H), 1.50-1.44 (m, 2H), 3.20 (t, J = 7.2 Hz, 2H), 4.14 (d, J = 2.4 Hz, 2H), 4.22 (d, J = 2.4 Hz, 2H), 4.64 (d, J = 2.4 Hz, 1H) ppm. 13C NMR (100 MHz; CDCl3) δ = 13.6, 19.5, 28.9, 43.5, 47.4, 85.9, 150.0, 155.2 ppm. GC-MS m/z (%) = 155 (90), 113 (27), 112 (100), 98 (11), 84 (37). 3-Methyl-5-methylene-1,3-oxazolidin-2-one (Compound 2b):[23] Yellow oil; 1H NMR (400 MHz; CDCl3) δ = 2.89 (s, 3H), 4.14 (dd, J = 2.4 Hz, 2H), 4.30 (dt, J = 3.1Hz, 1H), 4.72 (dt, J= 3.1 Hz, 1H) ppm. 13C NMR (100 MHz; CDCl3) δ = 30.4, 50.8, 86.5, 149.0, 156.1 ppm. 3-Methyl-5-ethylidene-1,3-oxazolidin-2-one (Compound 2c):[24] White powder; mp 74-76 ºC. 1H NMR (400 MHz; CDCl3) δ = 1.64 (dt, J = 7.0 Hz, 3H), 2.89 (s, 3H), 4.10 (dq, J = 2.2 Hz, 2H), 4.60 (qt, J = 7.0 Hz, 1H) ppm.

13

C NMR (100 MHz; CDCl3) δ = 9.6, 30.3, 50.0,

97.3, 141.3, 156.0 ppm. 3-Benzyl-5-ethylidene-1,3-oxazolidin-2-one (Compound 2d):[25] White powder; mp 40-42 ºC. 1H NMR (400 MHz; CDCl3) δ = 1.65 (dt, J = 7.0 Hz, 3H), 3.92 (dq, J = 2.2 Hz, 2H), 4.42 (s, 2H), 4.53 (qt, J = 7.0 Hz, 1H), 7.24-7.40 (m, 5H, Ar) ppm. 13C NMR (100 MHz; CDCl3) δ = 9.9, 47.4, 47.9, 97.9, 128.0, 128.8, 135.2, 141.6, 156.3 ppm.

3-Isopropyl-5-ethylidene-1,3-oxazolidin-2-one (Compound 2e):[26] Yellow oil; 1H NMR (400 MHz; CDCl3) δ = 1.15 (d, J = 6.5 Hz, 6H), 1.69 (dt, J = 6.9 Hz, 3H), 4.02 (dq, J = 2.2 Hz, 2H), 4.12 (septet, J = 6.7 Hz, 1H), 4.60 (qt, J = 7.0 Hz, 1H) ppm. 13C NMR (100 MHz; CDCl3) δ = 9.9, 19.7 ,42.9, 44.8, 97.3, 142.1, 155.3 ppm. 3-Methyl-5-benzylidene-1,3-oxazolidin-2-one (Compound 2f):[27] White powder; mp 139141 ºC. 1H NMR (400 MHz; CDCl3) δ = 2.94 (s, 3H), 4.30 (d, J = 2.1Hz, 2H), 5.49 (t, J = 2.1 Hz, 1H), 7.19 (t, J = 7.3Hz, 1H), 7.30 (dd, J = 7.3 Hz, J = 7.6 Hz, 2H), 7.54 (d, J = 7.6 Hz, 1H) ppm.

13

C NMR (100 MHz; CDCl3) δ = 30.5, 50.9, 102.9, 127.0, 128.2, 128.7, 133.5,

141.7, 155.6 ppm.

5-(40-Methylbenzylidene)-3-methyl-1,3-oxazolidin-2-one

(Compound

2g):[27]

White

powder; mp 134-136 oC. 1H NMR (400 MHz; CDCl3) δ = 7.47 (d, J = 8.1 Hz, 2 H), 7.15 (d, J = 8.0 Hz, 2 H), 5.50 (t, J = 2.0 Hz, 1 H), 4.30 (d, J = 2.0 Hz, 2 H), 3.00 (s, 3 H), 2.31 (s, 3 H). C NMR (100 MHz; CDCl3) δ = 155.6, 140.6, 136.3, 130.5, 129.0, 127.9, 102.9, 50.8, 30.2,

13

21.0 ppm. 5-benzylidene-3-butyl-4-ethyloxazolidin-2-one (Compound 2h):[22] Yellow oil; 1H NMR (400 MHz; CDCl3) δ = 1.09 (m, 6H), 1.31-1.40 (m, 2H), 1.52-1.59 (m, 2H), 1.73-1.75 (m, 1H), 1.97-2.01 (m, 1H), 3.01-3.06 (m, 1H), 3.54-3.65 (m, 1H), 4.54 (s, 1H), 5.50 (s, 1H), 7.20 (dd, J = 6.8 Hz, J = 12.8 Hz, 1H), 7.34 (dd, J = 7.2 Hz, J = 12.8 Hz, 2H), 7.61 (d, J = 7.6 Hz, 2H) ppm.

13

C NMR (100 MHz; CDCl3) δ = 6.3, 13.5, 20.1, 25.0, 29.1, 41.0, 58.9, 102.2,

126.5, 128.1, 133.8, 146.6, 155.3 ppm. GC-MS m/z (%) = 259 (14), 230 (100), 174 (51), 118 (26), 90 (22).

Results and discussion The HPG@KCC-1/PPh2/Au NP was prepared through the ringopening polymerization of glycidol on the surface of KCC-1 to form HPG@KCC-1 and then condensation of chlorodiphenylphosphine with HPG@KCC-1 as a template. The material was then reacted with a substoichiometric amount of sodium tetrachloroaurate (III) hydrate to yield the HPG@KCC-1/PPh2/Au NP catalyst. (Scheme 2).

The morphologies and structural features of KCC-1, and HPG@KCC-1/PPh2/Au NPs was evaluated using TEM images. The as prepared KCC-1 microsphereswith fibrous structure were uniform and monodispersed (Figure 1a).The average diameter of the microspheres was about 150-170 nm. TEM image shown in figure 1a further clarifies that the distance between the two fibers was about 10-15 nm. The TEM image of the HPG@KCC-1/PPh2/Au NPs are shown in figure 1b. The functionalization of the HPG@KCC-1/PPh2/Au NPs does not result in the change of the morphology and size of the obtained KCC-1 NPs. The recyclablity test was stopped after ten runs. Comparison of TEM images of used catalyst (Figure 1c) with those of the fresh catalyst (Figure 1b) showed that the morphology and structure of HPG@KCC-1/PPh2/Au NPs remained intact after ten recoveries. Low agglomeration of HPG@KCC-1/PPh2/Au NPs can be seen. FT-IR spectroscopy was employed to determine the surface modification of the synthesized catalyst (Figure 2). The Si-O-Si symmetric and asymmetric stretching vibrations at 802 cm−1 and 1103 cm−1 and the O-H stretching vibration at 3444 cm−1 were observed for the KCC-1 (Figure 2a). After the ringopening polymerization of glycidol on the surface of KCC-1, one band at 2931 cm−1 associated with C-H stretching significantly enhanced. Meanwhile, two new bands at 1486 and 1568 cm−1 associated with C-H and C-C stretching appeared, respectively (Figure 2b). The FT-IR shows three bands at around 1628 and 756 cm-1, which are presumably due to asymmetric stretching, and symmetric stretching modes of Si-O-Si, respectively. The peaks at 1612 and 1407 cm-1 are to confirm the presence of acetate ligand in the structure of HPG@KCC-1/PPh2/Au catalyst. Also, the peaks positioned at 1056 cm-1 related to the formation of P-O bond. Consequently, PPh2 groups were connected to the KCC-1 support by an O-linker (Figure 2c). The structural properties of synthesized HPG@KCC-1/PPh2/Au NP was analyzed by X-ray power diffraction (XRD) (Figure 3). The wide hump in the range of 2θ from 15 to 30o was characteristics of the amorphous silica of HPG@KCC-1 (Figure 3a). Figure 3b and 3c shows a typical XRD pattern of the HPG@KCC-1/PPh2 and HPG@KCC-1/PPh2/Au NP that there was no change in it. The thermal behavior of HPG@KCC-1/PPh2/Au NP is shown in figure 4. A significant decrease in the weight percentage of the HPG@KCC-1/PPh2/Au NP at about 130 °C is related to desorption of water molecules from the catalyst surface. This was evaluated to be 1-3 % ac-cording to the TG analysis. In addition, the analysis showed two other decreasing

peaks. First peak appears at temperature around 250-280 °C due to the decompo-sition of organic group and phosphine derivatives (Figure 4a and b). This is followed by a second peak at 420-620 °C, corresponding to the loss of the gold (Figure 4c). First, we examined the effect of solvent on the synthesis of 2-oxazolidinone from the propargylic amine and CO2 using the HPG@KCC-1/PPh2/Au NPs at 1.5 atm and heating under reflux (Table 1). Solvent does affect on catalysts performance. n-Hexane, an non-polar solvent, gave 2-oxazolidinone in a lower yield than that obtained in under solvent-free conditions (Table 1, entry 9 and 15). CH3CN, THF, CH2Cl2, DMF, Toluene, Dioxane, CHCl3, EtOAc, and DMSO, aprotic polar solvents, gave also 2-oxazolidinone in low yields. These results suggest that the aprotic polar solvents can't activate the propargylic amine. The reaction was do better in protic solvent. i-PrOH and ethanol gave 2-oxazolidinone in average yields (Table 1, entries 12 and 14). In contrast, the use of methanol resulted in an increased yield of 72%, and the yield was remarkably increased up to 92% when H 2O was used as the solvent. The protic solvents can activate the propargylic amine via hydrogen bonds formed between the hydroxyl and the acetylene groups. In this study, it was found that water is a more efficient (Table 1, entry 2) over other organic solvents.

At this stage, the amount of catalyst necessary to promote the reaction efficiently was examined. It was observed that the variation for HPG@KCC-1/PPh2/Au NP had an effective influence. The best amount of HPG@KCC-1/PPh2/Au NP is 0.1 mg which afforded the desired product in 92% yields (Figure 5). Under the optimal conditions, the reaction progress in the presence of 0.1 mg of HPG@KCC-1/PPh2/Au NP was monitored by GC. Using this catalyst system, excellent yields of 2-oxazolidinone can be achieved in 20 h (Figure 6). No apparent by-products were observed by GC in all the experiments and the 2-oxazolidinone was obtained cleanly in 92 % yield. We also investigated the crucial role of temperature and pressure in the fixation of CO2 with propargylic amine in the presence of HPG@KCC-1/PPh2/Au NPs as a catalyst. Clearly indicated that the catalytic activity was not sensitive to reaction temperature. The best temperature for this reaction was at room temperature. Temperatures greater than room temperature does not cause changes in the efficiency of the reaction. Pressure is a significant parameter with respect to safety concerns and connected costs, especially for industrial plants. Hence, the conversion at low pressures is desirable. To investigate the effect of

pressure, the conversion of propargylic amine was examined at 0–1.5 bar CO2 pressure and under isobaric conditions (Figure 7). In the pressure range of 0.5–1.5 bar, there was no notable effect of pressure on the yield of 2-oxazolidinone in the presence of HPG@KCC1/PPh2/Au NPs (Figure 7a). These results indicate that the synthesis of 2-oxazolidinone in the presence of KCC-1/PPh2/Au NP had already been performed in good yields (88%) with a constant more pressure (≥ 1.1 bar) (Figure 7b). However, by performing the reaction at extremely low pressures (≤ 0.5 bar), conversions and yields decreased significantly to 0 %. This prominent catalytic performance of HPG@KCC-1/PPh2/Au as compared with KCC1/PPh2/Au might be attributed to a great extent to the crucial promoting effect of confined HPG in obtaining high catalytic activity possibly through suppressing the catalyst deactivation and enabling easy CO2 delivery via a phase transfer mechanism. It should be noted that the promoting effect of HPG on the catalyst performance is however closely dependent on its content inside the fibrous of catalyst. To further evaluate the efficiency of the catalyst, different control experiments were performed and the obtained data is shown in Table 2. Firstly, one separated reaction was examined in the presence of KCC-1 NPs. The result of this studies showed that any amount of the desired product was not formed (Table 2, entries 1). When HPG@KCC-1 or HPG@KCC-1/PPh2 was used as the catalyst, a reaction was not still observed (Table 2, entries 2 and 3). Based on these frustrating results, we continued the research to improve the yield of the product by the optimization of the reaction conditions. To our delight, the reaction performed smoothly with the use of HPG@KCC-1/PPh2/Au and KCC-1/PPh2/Au NPs as the catalyst, and the HPG@KCC-1/PPh2/Au NP was more effective than KCC1/PPh2/Au (Table 2, entries 4 and 5). As a result, HPG@KCC-1/PPh2/Au NP was used in the subsequent investigations because of its high reactivity. The loading amount of gold (III) in HPG@KCC-1/PPh2/Au and KCC-1/PPh2/Au NPs as determined by inductively coupled plasma mass spectrometry (ICP-MS). The amount of gold (III) in HPG@KCC-1/PPh2/Au was almost equal KCC-1/PPh2/Au NPs. But it is interesting that this amount after reused for ten consecutive cycles of catalysts. The amount of gold (III) in HPG@KCC-1/PPh2/Au was about double KCC-1/PPh2/Au NPs. This remarkable ability of the HPG@KCC-1/PPh2/Au mesostructure may be attributed to HPG units that effectively manage the reaction through preventing Au agglomeration and releasing and recapturing gold during reaction process (Table 3). The carboxylative cyclization for a variety of propargylic amines was then undertaken to explore the scope of this well developed HPG@KCC-

1/PPh2/Au NP catalytic system. As shown in Table 4, both aromatic and aliphatic propargylic amines performed smoothly to give the corresponding 2-oxazolidinones in excellent yields. At this study, we evaluated the recoverability and reusability of the heterogeneous catalyst, according to green chemistry viewpoint. After fulfillment of the reaction, the catalyst was retrieved using was separated by filtration under vacuum. The HPG@KCC-1/PPh2/Au washed two times with ethanol and dried at 60 °C for 1h. The isolated catalyst was reused in subsequent reaction mixture under similar conditions. The catalyst retrieved up to ten times without tolerating any considerable decline in its catalytic activity or the efficiency of the reaction (Figure 8). Although, no significant performance in the activity of the catalyst was observed, to test if any gold (III) is leached from the solid catalyst during the process, a hot filtration test was performed for the reaction of propargylic amine, and CO2 after ~ 49% of the coupling reaction is completed. Interestingly, we found that whereas no propargylic amine, and CO2 species was detected by using atomic absorption spectroscopy in the filtrate. Also, In order to know whether the reaction takes place at the surface of HPG@KCC1/PPh2/AuNPs any gold species, ICP-MS analysis of the remaining mixture after catalyst and product separation was investigated upon reaction completion. The amount of gold after the ten repeated recycling was 3.6 % and the amount of gold leaching into the reaction mixture is very low. These observations indicated that the catalyst was stable and could tolerate the present reaction conditions.

Conclusions In summary, the design and preparation of a novel gold (III) phosphorus complex containing HPG-based ordered mesofibers organosilica (HPG@KCC-1/PPh2/Au) and its catalytic application for the cyclization of propargylic amines with CO2 to provide 2-oxazolidinones. Interestingly, it was found that while hot filtration tests and selective catalyst poisons showed the presence of soluble Au species during the reaction process, recovery studies illustrated that no significant decrease has occurred in the activity and metal content of recovered KCC1/IL/Au. In addition, the catalyst could be recovered and reused at least ten times with no decrease in its activity and selectivity. Based on these results, we conclude that although the HPG@KCC-1 nanostructure acts as cobweb for the soluble Au species, it can also operate as a nanoscaffold to retake the gold (III) into the mesofibrs, Thereby avoiding wide agglomeration of gold (III) phosphorus complex. This superior effectiveness of HPG@KCC1/PPh2/Au nanocatalyst may be ascribed to isolated HPG units incorporated in the mesofibrs

which could control the reaction mechanism through preventing the formation of agglomerated gold (III) phosphorus complex as well as stabilization of active catalytic gold species.

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Figure 1 TEM image of the fresh KCC-1 NPs (a), HPG@KCC-1/PPh2/Au NPs (b), and HPG@KCC-1/PPh2/Au NPs after ten reuses (c).

Figure 2 FTIR spectra of KCC-1 NPs (a), HPG@KCC-1 NPs (b), HPG@KCC-1/PPh2/Au NPs (c).

Figure 3 XRD analysis of HPG@KCC-1 (a), HPG@KCC-1/PPh2 (b), HPG@KCC-1/PPh2/Au NPs (c).

Figure 4 TGA diagram of HPG@KCC-1 (a), HPG@KCC-1/PPh2 (b), HPG@KCC-1/PPh2/Au NPs (c).

100 90 80

Yield (%)

70 60 50 40 30 20 10 0 0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

HPG@KCC-1/PPh2/Au (mg) Figure 5 Effect of increasing amount of HPG@KCC-1/PPh2/Au NPs on the preparation of 2-oxazolidinone.

Yield (%)

100 90 80 70 60 50 40 30 20 10 0 0

5

10

15

Time (h) Figure 6 Effect of time on yield of 2-oxazolidinone.

20

25

30

Figure 7 Effect of pressure on yield of 2-oxazolidinone. (a) HPG@KCC-1/PPh2/Au; (b) KCC-1/PPh2/Au.

100

Yield (%)

95 90 85 80 75 70 1

2

3

4

5

6

Reuse

Figure 8 Reuses performance of the catalysts.

7

8

9

10

Cl

PPh2 Au

Ph2P

Cl HO

Cl

O O

OH OH

HO O

O

HO

O

O

O OH O

O

HO O

HN R3 CO2

+

HO HO

OH

R2

N R3

O

R1 R1

R2

1 a-h

2 a-h

Scheme 1 Synthesis of 2-oxazolidinone in the presence of HPG@KCC-1/PPh2/Au NPs.

OEt O

EtO

Si

HO

OH

OH

OEt

O

HO

O OH

HO

OH

O

O

O

OEt

OH

O O

O

O

OH HO

HO

(KCC-1) ClPPh2

Cl

PPh2 Ph2P

Au

PPh2

NaAuCl4 O O

O HO

O

O OH O

O OH

O

O

O

O

OH O

O

HO OH

O

OH HO

HO O

OH

HO

HO

Cl

OH

O

Cl

O

OH HO

HO

HO O

HO HO

OH

Scheme 2 Schematic illustration of the synthesis for HPG@KCC-1/PPh2/Au NPs.

Table 1 Synthesis of 2-oxazolidinone by HPG@KCC-1/PPh2/Au NPs in different solvents.a Entry

Solvent

Yield (%)b

1

EtOH

64

2

H2O

92

3

CH3CN

-

4

THF

23

5

CH2Cl2

31

6

EtOAc

42

7

DMF

15

8

Toluene

29

9 10

n-Hexane CHCl3

17 40

11

DMSO

38

12

MeOH

72

13

Dioxane

16

14

i-PrOH

59

15

solvent-free

38

a

Reaction conditions: propargylic amine (1 mmol), HPG@KCC-1/PPh2/Au NPs (0.002 g), and CO2 1.5 MPa, under reflux of solvents after 48 hour. b Isolated yields.

Table 2 Influence of different catalysts for the synthesis of 2-oxazolidinone.a

a

b

Entry

Catalyst

Yield (%)b

1

KCC-1

-

2

HPG@KCC-1

-

3

HPG@KCC-1/PPh2

-

4

HPG@KCC-1/PPh2/Au

92

5

KCC-1/PPh2/Au

88

Reaction conditions: propargylic amine (1 mmol), catalyst (0.001 g), and CO2 1.5 MPa, in water at room temperature after 24 hour. Isolated yield.

Table 3 The loading amount of nano gold in HPG@KCC-1/PPh2/Au, and KCC-1/PPh2/Au NPs. Entry

Catalyst

wt %

1

KCC-1/PPh2/Au

3.3

2

HPG@KCC-1/PPh2/Au

3.7

3

KCC-1/PPh2/Au after ten reuses

1.9

4

HPG@KCC-1/PPh2/Au after ten reuses

3.6

Table 4 Synthesis of 2-oxazolidinone derivatives catalyzed by HPG@KCC-1/PPh2/Au NPs.a Entry

R1

R2

R3

Product

Yield (%)b

1

H

H

CH3CH2CH2CH2

2a

86

2

H

H

CH3

2b

89

3

CH3

|H

CH3

2c

81

4

CH3

H

C6H5CH2

2d

90

5

CH3

H

(CH3)2CH

2e

87

6

C6H5

H

CH3

2f

92

7

4-CH3C6H4

H

CH3

2g

94

8

C6H5

CH3CH2

CH3CH2CH2CH2

2h

93

a

Reaction condition: propargylic amine derivatives (1 mmol), catalyst (0.1 mg), and CO 2 0.5 MPa, in water at room temperature after 20 hour. b

Yield refers to isolated product.