DOI: 10.1002/cctc.201200578

Copper-Incorporated Porous Polydivinylbenzene asEfficient and Recyclable Heterogeneous Catalyst inUllmann Biaryl Ether CouplingLiang Wang,[b] Jian Zhang,[a] Jing Sun,[b] Longfeng Zhu,[b] Haiyan Zhang,[b] Fujian Liu,[b]

Dafang Zheng,[b] Xiangju Meng,[a] Xiaodong Shi,*[c] and Feng-Shou Xiao*[a]

Introduction

Compared with the solution-based homogeneous catalysis, thesolid-support heterogeneous catalysis has some clear advan-tages, such as the easier operation/purification and catalyst re-usability.[1–7] Thus, the heterogeneous catalysis is widely usedin industrial processes for fine chemical synthesis.[8–10] Themost popular strategy used currently in conducting the heter-ogeneous catalysis is the introduction of the catalytic centerson the solid surface, which will enable the reaction to occurbetween the solid support and the substrate interface.[11, 12]

Therefore, compared with the similar homogeneous catalysis,the heterogeneous catalysis usually suffered from decreasedreactivity owing to the less effective interactions between cata-lytic centers and reactants.[13, 14] This is challenging for transi-tion metal-promoted organic transformations, in which a good

mix between catalysts and substrates is often required for ef-fective reactions.[13]

The fast-growing research on inorganic porous materials of-fered some unique features as a new type of solid support forheterogeneous catalysis.[15–29] By providing the “open” spaceinside the solid support, the porous materials enabled the cat-alyst–reactant interactions with much higher efficiency. Twogood examples of these porous materials reported in the liter-ature that have been used in catalysis are zeolite-[15–18] andmesoporous silica-[20–29] based porous materials. The porous or-ganic polymers have attracted much attention because theyare very easy to prepare on a large scale under mild conditionscompared with other types of porous materials reported in theliterature, which were usually synthesized with expensive or-ganic surfactants or templates, and calcination at high temper-ature is usually required to obtain opening channels.[20, 22, 30–33]

In addition, owing to the inherited nature of the organic pores,the “cavities” of the organic polymers are the best mimic ofthe chemical environment in the organic solvent-mediated ho-mogeneous catalysis and thus help in the maintenance of thecatalyst reactivity.

The Xiao group reported the preparation and application ofsuperhydrophobic porous polydivinylbenzene (PDVB) as an ef-fective adsorbent for various organic compounds.[32–33] Thesesuccesses initiated our interest in extending the use of porousorganic polymer PDVB to the more challenging transitionmetal catalysis, which formed the highly desired heterogene-ous organomatellic catalysts. Over the last several years, sever-al examples of polymer-supported catalysts have been report-ed in the literature.[34–39] However, in most of these cases, non-porous polymers and porous polymers with low porosity and

The preparation of efficient and stable heterogeneous catalystis very important for organic transformations. Herein, wereport a copper-incorporated porous, Schiff base-modified pol-ydivinylbenzene (PDVB-SB-Cu) as an excellent heterogeneouscatalyst in promoting Ullmann biaryl ether coupling reactions.PDVB-SB-Cu was synthesized by incorporating copper speciesinto PDVB-SB. Combined characterizations by using 13C NMR,IR, XPS, N2 adsorption, and TEM indicated the synthesis ofcopper–Schiff base species on porous PDVB. Catalytic tests inthe Ullmann biaryl ether coupling of iodobenzene and phenol

indicated that the PDVB-SB-Cu catalyst gave high activity simi-lar to that of the homogeneous Schiff base-stabilized coppercatalyst. This good reactivity was likely due to the polymer-based porous materials, which provided more effective interac-tions between substrates and catalytic centers. Importantly,PDVB-SB-Cu has extraordinary recyclability. The advantages ofhigh activities and good recyclability made the PDVB-SB-Cucatalyst a new class of solid-support transition metal catalystsfor fine chemical preparation.

[a] J. Zhang, Dr. X. Meng, Prof. F.-S. XiaoKey Lab of Applied Chemistry of Zhejiang ProvinceZhejiang UniversityHangzhou 310028 (P. R. China)Fax: (+ 86) 431-85168624E-mail : fsxiao@zju.edu.cn

[b] L. Wang, J. Sun, L. Zhu, H. Zhang, F. Liu, D. ZhengLaboratory of Inorganic Synthesis and Preparative ChemistryJilin UniversityChangchun 130012 (P. R. China)

[c] Prof. X. ShiDepartment of ChemistryWest Virginia UniversityMorgantown, MV 26506 (USA)E-mail : Xiaodong.Shi@mail.wvu.edu

Supporting information for this article is available on the WWW underhttp://dx.doi.org/10.1002/cctc.201200578.

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surface area were used generally, which limited the interactionbetween substrates and catalytic sites (less effective comparedto homogeneous reactions).[34, 35] Herein, we report the incorpo-ration of copper cations into the pores of Schiff base-modifiedPDVB (PDVB-SB-Cu) used as an effective solid-supported cata-lyst in promoting Ullmann biaryl ether coupling with high effi-ciency and excellent reusability.

Results and Discussion

Synthesis and characterization of PDVB-SB-Cu

As shown in Scheme 1, the general design of the PDVB-SB-Cucatalyst was to modify the porous PDVB through sequential ni-

tration and reduction to obtain NH2-grafted PDVB (PDVB-NH2).The formation of the Schiff base-modified PDVB (PDVB-SB) wasachieved through refluxing PDVB-NH2 with the correspondingpyridinecarboxaldehyde. PDVB-SB, which possessed bidentatenitrogen-binding sites, was then reacted with copper cations,which yielded the copper-incorporated heterogeneous catalyst(PDVB-SB-Cu; 1.4 wt % of copper).

The PDVB-SB-Cu catalyst was characterized by using13C NMR spectroscopy (Figure 1). The signal at 41 ppm was at-tributed to the aliphatic chain on PDVB.[40] The strong signalsat 128 and 144 ppm associated with the carbon on the aro-matic ring.[41] The weak signals at 113 and 135 ppm were at-tributed to the residual vinyl groups, which indicated the highdegree of cross-linking in the framework.[40, 42] The additionalsignal at 149 ppm for PDVB-SB-Cu suggests the formation ofthe C=N bond in the presence of Schiff base.[43]

The IR spectra confirmed further the functional groups(Figure 2). Compared with PDVB, PDVB-SB indicated the addi-tional absorption at 1524 cm�1, which supported the presence

of the C�N bond.[44, 45] The signal at 1624 cm�1 was the charac-teristic absorption associated with the C=N bond in Schiffbases.[46, 47] Notably, this C=N bond absorption gave a clear red-shift for the sample of PDVB-SB-Cu (1607 cm�1), which suggest-ed the strong interaction between nitrogen atoms in the Schiffbase and copper cations.[48–50] The band at 471 cm�1 associatedwith the Cu�N bond in PDVB-SB-Cu also confirmed thisinteraction.[48, 51]

Scheme 1. Synthesis of copper-incorporated porous organic polymercatalyst.

Figure 1. 13C NMR spectra of a) PDVB and b) PDVB-SB-Cu.

Figure 2. IR spectra of the porous polymers: a) PDVB, b) PDVB-SB, andc) PDVB-SB-Cu.

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The N 1s XPS spectra of these synthesized polymers areshown in Figure 3A. PDVB-NH2 gave a peak at 399.4 eV, whichindicated the presence of the NH2 group.[52] In comparison, thespectrum of PDVB-SB indicated a peak at 398.9 eV, witha downshift of 0.5 eV from PDVB-NH2, which was assigned tothe formation of the C=N bond.[53, 54] After the loading ofCu(OAc)2, the binding energy of N 1s shifted back to 399.4 eV,which indicated the interactions between the Schiff base andCu(OAc)2. These results were in good agreement with structureassignments obtained from the IR spectra. The Cu 2p XPS spec-tra of PDVB-SB-Cu and Cu(OAc)2 are depicted in Figure 3 B and

C. The spectrum of Cu(OAc)2 gave a binding energy of Cu 2p3/2

at 933.8 eV, and Cu 2p3/2 and Cu 2p1/2 peaks were accompaniedby intense satellite features at approximately 942.0 and962.0 eV, which were assigned to typical Cu2 + .[55–57] PDVB-SB-Cu gave a binding energy of Cu2p3/2 at 932.9 eV, which re-duced the binding energy of Cu2+ at 0.9 eV with a disappear-ance of 942 and 962 eV in Cu(OAc)2, which was assigned toCu+ or metallic Cu species.[58–60] Furthermore, the Cu (LMM)Auger XPS spectrum of PDVB-SB-Cu (Figure 3C) gave the kinet-ic energy at 915.6 eV, which indicated the presence of Cu+ inPDVB-SB-Cu.[61, 62]

The porous nature of PDVB and copper-incorporated PDVB-SB-Cu was also investigated. The nitrogen isotherms of PDVB,PDVB-NH2, PDVB-SB, and PDVB-SB-Cu samples (Figure 4) gave

typical type IV curves with a hysteresis loop at a relative pres-sure of 0.48<P/P0<0.98, which indicated the presence of po-rosity in these samples. Notably, PDVB demonstrated high sur-face area (627 m2 g�1), whereas PDVB-NH2, PDVB-SB, and PDVB-SB-Cu showed relatively low surface area (210–250 m2 g�1). Thisphenomenon was consistent with the proposed modification.In addition, the SEM and TEM (Figure 5) images provided thedirect observation of rich porosity in both PDVB andPDVB-SB-Cu.

Figure 3. A) N 1s, B) Cu 2p, and C) Cu LMM Auger XPS spectra. a) PDVB,b) PDVB-NH2, c) PDVB-SB, d) PDVB-SB-Cu, and e) Cu(OAc)2.

Figure 4. Nitrogen isotherms of porous polymers: a) PDVB, b) PDVB-NH2,c) PDVB-SB, and d) PDVB-SB-Cu.

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Ullmann biaryl ether coupling on copper catalysts

After the copper-incorporated porous polymer was synthesizedand characterized, the reactivity of this new type of solid-sup-port transition metal catalyst was investigated. One copper-promoted reaction of particular interest was the Ullmann biarylether coupling reaction: First, the coupling reaction was one ofthe most important basic transformations in organic synthesisbecause it could bring functional groups together in a directfashion and thus achieve complex molecules in simple steps.Second, compared with the well-developed palladium cou-pling reactions, the copper-catalyzed reactions were muchcheaper, which were more suitable for large-scale fine chemicalproduction. Currently, the main challenge of the copper-cata-lyzed reaction was its low efficiency. It has been reported thatthe ligand played a crucial role in copper-catalyzed reac-tions.[63, 64] With these concerns in mind, we started our investi-gation of different catalysts in promoting coupling betweenphenyl iodide and phenol. The results are summarized inTable 1.

As shown in Table 1, the simple copper(II) salts catalyzed thisreaction but with poor performances (entries 1–3). The Schiffbase ligand-coordinated SB-Cu catalyst gave significantly im-proved reactivity, which in turn gave the coupling product in95 % yield (entry 4). The solid-support porous PDVB-SB-Cu cata-lyst indicated comparable reactivity to the homogeneous ana-

logues, which gave the desired products in excellent yield(entry 5). In contrast, the nonporous PDVB (prepared throughthe hydrothermal polymerization of DVB in a solvent-freesystem) supported the SB-Cu catalyst (nonporous PDVB-SB-Cu),which indicated significantly lower reactivity (69 % yield;entry 6) owing to the less effective interaction between thecatalytic center and the reacting substrates.[65]

In addition, the PDVB-SB-Cu catalyst was treated in DMSO at115 8C for 16 h. After filtration of the PDVB-SB-Cu catalyst, thesolution was used as the new catalyst for Ullmann biaryl ethercoupling. Thus, no products were found. The concentration ofcopper in the treated solution was less than 0.01 ppm, whichwas determined from inductively coupled plasma (ICP) analy-sis. These results indicate that no copper leaching occurred onthe PDVB-SB-Cu catalyst during the Ullmann coupling reaction.Furthermore, the PDVB-SB-Cu catalyst showed good reusability,and good reactivity was observed even if the catalyst was recy-cled six times (entries 8 and 9).[66]

The fact that the nonporous PDVB-SB-Cu catalyst gave muchlower yield highlighted the importance of the pores in this cat-alyst design. The other important aspect of the polymer-basedsolid-support catalyst was the “organic-like microenvironment”compared with other inorganic material-based porous cata-lysts. To verify this hypothesis, a comparison with inorganicmaterial-based porous materials MCM-41-SB-Cu was made(Table 2).

The silica oxide-based porous material MCM-41 (orderedmesoporous silica with the p6mm structure) was modified toform the MCM-41-SB-Cu catalyst by using a similar process(see the scheme in the Supporting Information). As shown inTable 1, entry 7, this solid support catalyst gave a significantlylower yield than did the PDVB-SB-Cu catalyst, even witha higher surface area (330 m2 g�1 vs. 210 m2 g�1; Table 2). Thecomparison of adsorption capacities between PDVB-SB-Cu andMCM-41-SB-Cu revealed a significantly higher absorption abili-ty of the polymer support than that of the inorganic materialsupport toward PhI and DMSO, which strongly supported our

Table 1. Copper-promoted Ullmann biaryl ether coupling.[a]

Entry Catalyst Yield[b]

[%]

1 Cu(OAc)2 522 CuCl2 403 CuSO4 314 SB-Cu 955 PDVB-SB-Cu 916 nonporous PDVB-SB-Cu 697 MCM-41-SB-Cu 748 2nd reuse 899 6th reuse 81

[a] Reaction conditions: 1 mmol of iodobenzene, 1 mmol of phenol,1 mmol of Cs2CO3, Cu catalysts (contains 0.2 mmol of Cu), 6 mL of DMSO,N2 atmosphere, 115 8C, 16 h, dodecane as internal standard; [b] GC yield,the error of yield is within 2 %.

Figure 5. SEM images of a, b) PDVB and c, d) PDVB-SB-Cu. TEM images ofe) PDVB and f) PDVB-SB-Cu. The scale bar are 10 mm, 1 mm, 10 mm, and100 nm for parts a–d, respectively.

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hypothesis that polymer-based porous materials providedbetter catalysts for organic transformation in heterogeneousprocesses.

The dependence of the catalytic yield of biphenyl ether ontime over the PDVB-SB-Cu catalyst in the Ullmann ether cou-pling of iodobenzene and phenol is shown in Figure 6. Theyield of biphenyl ether decreased with time and reached 91 %

in 16 h with 20 mol % of copper. The reaction time could notincrease the product yield further. In addition, similar etheryield (88 %) could be obtained in a long reaction time of 24 hover the catalyst with 10 mol % of copper. The catalyst with2 mol % of Cu showed very low activity with ether yield atmost of 17 %. Thus, more copper amount could lead to highproduct yield in short reaction time.

We tested several different bases for the Ullmann ether cou-pling of iodobenzene and phenol over the PDVB-SB-Cu cata-lyst. Cs2CO3 was found to be the most active (Table 3, entry 1),and other bases K2CO3, K3PO4, NaOH, and triethylamine allgave low activity, with a product yield of 35–80 % (Table 3, en-tries 2–5). In addition, the effect of the solvent on the couplingreaction was investigated. In DMSO, a high yield of products(91 %; Table 4, entry 1) could be obtained. DMF led to a loweryield of 77 % (Table 4, entry 2). Low product yields at less than

8 % was obtained in toluene, ethanol, and H2O (Table 4, en-tries 3–5). Furthermore, the dependence of the catalytic yieldof biphenyl ether on reaction temperature for this reaction isshown in Figure 7. No desired product was obtained at a lowtemperature of 70 8C, and the product yield increased with thereaction temperature until 115 8C, in which a high yield of 91 %could be obtained. A higher reaction temperature of 130 8C

Table 2. Textural parameters and adsorption capacities.

Sample SBET

[m2 g�1]Adsorption capacity[a]

[g g�1]PhOH PhI DMSO

PDVB-SB-Cu 210 4.7 5.1 3.9(NP)PDVB-SB-Cu <10 – – –MCM-41-SB-Cu 330 4.2 2.1 1.4

[a] Adsorption capacity of phenol was tested at 73 8C, and adsorption ca-pacities of iodobenzene and DMSO were tested at RT.

Figure 6. Dependence of yield of biphenyl ether on time over PDVB-SB-Cuwith different catalyst amounts in the Ullmann ether coupling of iodoben-zene and phenol. Reaction conditions are the same as those given inTable 1.

Table 3. Effect of base on Ullmann biaryl ether coupling.[a]

Entry Base Yield[b]

[%]

1 Cs2CO3 912 K2CO3 793 K3PO4 354 NaOH 805 triethylamine 51

[a] Reaction conditions: 1 mmol of iodobenzene, 1 mmol of phenol,1 mmol of base, PDVB-SB-Cu (contains 0.2 mmol of Cu), 6 mL of DMSO,N2 atmosphere, 115 8C, 16 h, dodecane as internal standard; [b] GC yield,the error of yield is within 2 %.

Table 4. Effect of solvent on the Ullmann biaryl ether coupling.[a]

Entry Solvent Yield[b]

[%]

1 DMSO 912 DMF 773 toluene 84 ethanol <15 H2O <1

[a] Reaction conditions: 1 mmol of iodobenzene, 1 mmol of phenol,1 mmol of Cs2CO3, PDVB-SB-Cu (contains 0.2 mmol of Cu), 6 mL of sol-vent, N2 atmosphere, 115 8C for DMF and DMSO, 110 8C for toluene, 78 8Cfor ethanol, and 100 8C for H2O, 16 h, dodecane as internal standard;[b] GC yield, the error of yield is within 2 %.

Figure 7. Dependence of yield of biphenyl ether on reaction temperatureover PDVB-SB-Cu with different catalyst amounts in the Ullmann ether cou-pling of iodobenzene and phenol. Reaction conditions are the same asthose given in Table 1.

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could not lead to an increase in the yield. Based on these re-sults, the optimized reaction conditions for this Ullmann biarylether coupling are the PDVB-SB-Cu catalyst (contains 20 mol %of copper) and Cs2CO3 in DMSO at 115 8C for 16 h.

Various aryl halides and substituted phenols were used withPDVB-SB-Cu as catalysts to verify the reaction substrate scope.As shown in Table 5, the catalyst worked well with a largegroup of different aryl iodides and substituted phenols, which

gave the desired coupling products in excellent yields. The io-dobenzene compounds with electron-withdrawing groupsmore easily coupled with phenol, which gave high yields of di-phenyl ether at 99, 99, and 86 % on p-NO2-, p-CN-, and p-Cl-modified iodobenzene, respectively (Table 5, entries 1–3). In ad-dition, the iodobenzene-containing electron-donating group p-CH3 indicated slightly lower activity with an ether yield of 80 %(Table 5, entry 4). On the other hand, phenols with both elec-tron-withdrawing and electron-donating groups on aromaticrings showed good activities in the Ullmann biaryl ether cou-pling with iodobenzene to produce the corresponding diphen-yl ether in good yields (89–93 %; Table 5, entries 5–7). Further-more, the aryl bromide was suitable for this reaction, whichfurther extended the reaction substrate scope (Table 5,entry 8). The aryl chloride was not suitable for this condition,however, similar to the homogeneous catalysis results reportedin the literature (Table 5, entry 9).[59, 60] The excellent reusabilitywas also observed for all reactions, which highlighted the clearadvantages of the heterogeneous catalysts over the homoge-neous catalysts.

Conclusions

A new type of copper-modified porous organic polymer-basedcatalyst was developed. The catalyst was readily prepared ona large scale from cheaper materials and was used as a highlyeffective catalyst in promoting Ullmann coupling. This new ma-terial adopted porous nature to enable effective interactionsbetween substrates and catalytic centers. In addition, com-

pared with inorganic material-based porous catalysts, the poly-mer-based catalysts best mimicked the reaction nature in thesolution phase, which gave significantly improved reactivity.The porous and hydrophobic nature of this new material of-fered a unique combination for effective catalytic–substrate in-teractions, which made the PDVB-SB-Cu catalyst a new class ofsolid-support transition metal catalysts for fine chemical prepa-ration. Considering the general reactivity of copper cations inorganic synthesis, it is expected that the reported PDVB-SB-Cucatalyst would likely help the synthesis of other copper-cata-lyzed organic transformations, which are currently underinvestigation.

Experimental Section

Synthesis of PDVB

PDVB was synthesized hydrothermally through the polymerizationof DVB. As a typical run, DVB (12 g) was added to DMF (120 mL),followed by the addition of azobisisobutyronitrile (0.3 g) and water(12 mL). After stirring at RT for 3 h, the mixture was transferred toan autoclave and treated hydrothermally at 100 8C for 48 h. ThePDVB sample was collected through the evaporation of DMF at RT.

Synthesis of PDVB-NH2

PDVB-NH2 was obtained through the nitration and reduction ofPDVB. As a typical run, PDVB (4.0 g) was poured into the mixtureof H2SO4 (98 %, 116 g) and HNO3 (65 %, 30 g). After stirring the mix-ture at 0 8C for 16 h in a methanol bath, PDVB-NO2 was formed.Then, the mixture was added to water (1.5 L). PDVB-NO2 was col-lected through filtration and washing with a large amount ofwater. The obtained PDVB-NO2 was stirred in HCl (10 m, 60 mL)with SnCl2 (6.5 g). After stirring at 27 8C for 3 days, PDVB-NH2 wasformed. Then, the mixture was added to water (1.5 L). The PDVB-NH2 sample was collected through filtration and washing witha large amount of 2-aminopropane and ethanol.

Synthesis of PDVB-SB-Cu

As a typical run, PDVB-NH2 (10 g) was added to toluene (100 mL).After stirring the mixture for 1 h, 2-pyridinecarboxaldehyde (25 mL)was added. After heating under reflux for 2 days, PDVB-SB was col-lected through filtration and washing with ethanol and water. Forthe preparation of the PDVB-SB-Cu sample, PDVB-SB (5 g) wasadded in acetone (40 mL). After stirring at RT for 1 h, the mixturewas heated to 50 8C. Then, the Cu(OAc)2 solution (80 mL) wasadded and the mixture was stirred overnight. Finally, the productof PDVB-SB-Cu was collected through filtration and washing withwater. The copper content of this sample determined from ICPanalysis was 1.4 wt %.

Synthesis of nonporous PDVB-SB-Cu

PDVBs without porosity (designated as nonporous PDVBs) weresynthesized hydrothermally through the polymerization of DVBwithout the addition of any solvent. As a typical run, azobisisobu-tyronitrile (0.3 g) was added to DVB (12 g). After stirring at RT for3 h, the mixture was transferred to an autoclave and treated hydro-thermally at 100 8C for 48 h. The nonporous PDVB sample was col-lected. Nonporous PDVB-SB-Cu was prepared in the same way as

Table 5. Catalytic properties of PDVB-SB-Cu on Ullmann biaryl ether cou-pling using various substrates.[a]

Entry Aryl halide Phenol Yield[b]

[%]1st run 5th run

1 p-NO2C6H4I C6H5OH 99 852 p-CNC6H4I C6H5OH 99 873 p-ClC6H4I C6H5OH 86 804 p-CH3C6H4I C6H5OH 80 775 C6H5I p-CH3C6H4OH 93 886 C6H5I p-CH3OC6H4OH 89 757 C6H5I p-ClC6H4OH 91 818 C6H5Br C6H5OH 71 709 C6H5Cl C6H5OH <1 –

[a] Reaction conditions: 1 mmol of iodobenzene, 1 mmol of phenol,1 mmol of Cs2CO3, Cu catalysts (contains 0.2 mmol of Cu), 6 mL of DMSO,N2 atmosphere, 115 8C, 16 h, dodecane as internal standard; [b] The errorof yield is within 2 %.

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PDVB-SB-Cu, except for using nonporous PDVB instead of PDVB.The copper content of this sample determined from ICP analysiswas 1.4 wt %.

Synthesis of MCM-41-SB-Cu

As a typical run (Scheme S1), cetyltrimethylammonium bromide(0.8 g) was dissolved in water (25 mL), NH3·H2O (12 mL), and tet-raethyl orthosilicate (4.5 mL). After stirring at RT for 24 h, the mix-ture was transferred to an autoclave for condensation at 100 8C for24 h. Then, the as-synthesized sample (as-synthesized MCM-41)was collected through filtration and washing in ethanol solventcontaining HCl. The as-synthesized MCM-41 (1 g) was dried at120 8C under vacuum for 3 h, followed by the addition of pretreat-ed toluene (50 mL) containing NH2CH2CH2CH2Si(OC2H5)3 (KH-550;1.2 g). The mixture was heated under reflux overnight and collect-ed through rotary evaporation, followed by washing with a largeamount of ethanol. The sample obtained was designated as MCM-41-NH2. The aforementioned experiments were performed in anhy-drous conditions to avoid the interaction between amine speciesand H2O. MCM-41-NH2 (1 g) was added in toluene (20 mL). Afterstirring the mixture for 1 h, 2-pyridinecarboxaldehyde (2.5 mL) wasadded. After heating under reflux for 24 h, the sample was collect-ed through filtration and washing with ethanol and water and des-ignated as MCM-41-SB. Next, MCM-41-SB (1 g) was added in water(50 mL). After stirring at RT for 1 h, the mixture was heated to50 8C, followed by the addition of Cu(OAc)2. After stirring over-night, the product was collected through filtration and washingwith ethanol and water, which was designated as MCM-41-SB-Cu.The copper content of this sample determined from ICP analysiswas 1.0 wt %.

Synthesis of SB-Cu

As a typical run, aminobenzene (10 g) was added in toluene(100 mL). Then, 2-pyridinecarboxaldehyde (11.5 g) was added. Afterheating the mixture under reflux for 48 h, DMSO (30 mL) wasadded, followed by rotary evaporation to remove toluene. The SB-Cu catalyst dissolved in DMSO was finally obtained by treatingCu(OAc)2 in the mixture at 60 8C for 4 h.

Characterization of the sample

13C NMR spectra were recorded on a Bruker Avance III 400 WBspectrometer by using CP-TOSS program with 7.5 mm of MASprobe, 12 kHz of spinning rate, repetition time of 3 s, and contacttime of 1 s. XPS spectra were recorded on a Thermo ESCALAB 250spectrometer, and the binding energy was calibrated by C 1s peak(284.9 eV). FTIR spectra were recorded on a Bruker 66V FTIR spec-trometer. TEM experiments were performed with a JEOL JEM-3010electron microscope operating at an acceleration voltage of300 kV. SEM experiments were performed with a JEOL JSM-6700Felectron microscope. Nitrogen isotherms at the temperature ofliquid nitrogen were measured with a Micromeritics ASAP (Tristar).The samples were outgassed at 150 8C for 10 h before the mea-surement. Pore-size distribution was calculated by using the Bar-rett–Joyner–Halenda model. The copper content was determinedfrom ICP analysis by using a Perkin–Elmer Plasma 40 emissionspectrometer.

Catalytic tests

Ullmann biaryl ether coupling was performed in a 20 mL glass re-actor with a magnetic stirrer (900 rpm). As a typical run, iodoben-zene (1 mmol), Cs2CO3 (1 mmol), copper catalysts (contains20 mol % of copper), and DMSO (6 mL) were mixed in the reactor.After stirring at RT for 30 min, phenol (1 mmol) was added, fol-lowed by increasing the temperature to 115 8C. The reaction pro-cess was performed under N2 atmosphere. After reaction, the prod-ucts were extracted and analyzed by using GC (GC-14C or GC-17A,Shimadzu) equipped with a flame ionization detector and a flexiblequartz capillary column (OV-17 or FFAP). The recyclable catalystwas collected by centrifugation of the reaction mixture, washingwith a large quantity of acetone, and drying at 80 8C overnight.

Acknowledgements

This work was supported by the State Basic Research Project ofChina (2009CB623507) and National Natural Science Foundationof China (20973079).

Keywords: heterogeneous catalysis · polymers · porousmaterials · recycling experiments · Ullmann coupling

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occurred during catalyst recycling. The slight loss of reactivity was likelycaused by the change in the copper cations, by which a small amountof the active catalyst Cu+ was converted to Cu2 + during the reaction.This was confirmed by Cu 2p and Cu LMM Auger XPS spectra of PDVB-SB-Cu after it was reused 5 times (see Figure S1 in the SupportingInformation).

Received: August 24, 2012

Published online on January 25, 2013

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