DOI: 10.1002/cctc.201000062

Cu Nanoparticles in PEG: A New Recyclable CatalyticSystem for N-Arylation of Amines with Aryl HalidesMazaahir Kidwai,*[a] Neeraj Kumar Mishra,[a] Saurav Bhardwaj,[a] Anwar Jahan,[a]

Ajeet Kumar,[b] and Subho Mozumdar[b]

Introduction

The N-arylation of NH-containing substrates is important inorganic synthesis because the resultant products, arylamines,and N-aryl heterocycles are ubiquitous compounds in pharma-ceuticals, crop protection chemicals, and material sciences.[1–4]

Hartwig,[5] Buchwald and co-workers,[6] and Shakespeare[7] havereported that arylation of amines, amides, and C�N bond form-ing cross-coupling reactions of NH-containing substrates hasemerged as a powerful methodology. Chan et al. ,[8] Evanset al. ,[9] Lam et al. ,[10] and others[11-13] reported that arylaminesand N-arylheterocycles can be prepared using boronic acids,cupric acetate [Cu(OAc)2] , and Cu0 catalysts under mild condi-tions compared to that of conventional Ullmann and Goldbergarylation protocols.[14] The synthetic scope of traditionalUllmann coupling protocols are greatly limited by its highreaction temperature (often 120 8C or higher)[14–16] and poorsubstrate generality. In addition, these reactions often requirethe use of stoichiometric amounts of reagents, which on scale,leads to problems of waste disposal. To overcome all thesedrawbacks, considerable attention has been paid to developan efficient and recyclable catalytic method for N-arylation.

In this context, polyethylene glycol (PEG) has been used as asolvent and phase-transfer catalyst (PTC) in organic synthesis.A number of recent reviews have also covered PEG chemistryand its applications in biotechnology and medicine,[17] PEG-supported catalysis,[18] PEG-based aqueous biphasic systems(ABS) as alternative separation media,[19] aqueous two-phasesystems (ATPS) in bioconversion,[20] and its derivatives as sol-vent and PTC in organic synthesis.[21] The toxicity profile andenvironmental burden are available for a range of PEG molecu-lar weights. The preliminary studies have revealed that PEGcould be used as a reaction medium for selective reactionswith easy recyclability.[22-23]

Despite the advantages of homogeneous metal catalysts,difficulties in recovering the catalyst from the reaction mixtureseverely inhibits their wide use in industry. Heterogeneouscatalysis supplies the opportunity for easy separation and

recycling of the catalyst, easy product purification, andpossibly, continuous or multiple processing of compounds.Thus, the development of improved synthetic methods forN-arylation remains an active research area.

Metal nanoparticles (NPs)[24, 25] as catalysts in synthetic or-ganic chemistry have gained much interest. Current literatureshows that the application of Cu nanoparticles as catalysts inorganic synthesis has been little explored. Copper nanoparti-cles are particularly attractive because they are high yielding,need mild reaction conditions, and are recyclable.[26, 27] Further-more, the use of copper nanoparticles, in Ullmann and Suzukicross coupling reactions[11, 28] are considered ecofriendly.

Heterogeneous metal nanoparticles find excellentapplication for various organic transformations.[29, 30] The highreactivity of metal nanoparticles is due to higher surfaceareas than the bulk metal catalyst. This is thought to be duemorphological differences; whereas large size metal catalystshave only a small percentage of reactive sites on the surface,smaller size nanoparticles will possess a much higher surfaceconcentration of such sites. The catalytic activity of Cu nano-particles was evident when no product was obtained in theabsence of the catalyst.

Considering our previous works in the field of metal nano-particles[29, 30] and PEG[22] in organic synthesis, we have devel-oped an efficient method for C�N bond formation using Cunanoparticles as catalyst in PEG with excellent yields. The reac-tion is effective at 95 8C in PEG in the presence of K2CO3. The

[a] Prof. M. Kidwai, N. K. Mishra, S. Bhardwaj, A. JahanGreen Chemistry Research Laboratory, Department of ChemistryUniversity of Delhi, Delhi-110007 (India)Fax: (+ 91) 11-2766-6235E-mail : kidwai.chemistry@gmail.com

[b] A. Kumar, Dr. S. MozumdarLaboratory for Nanobiotechnology, Department of ChemistryUniversity of Delhi, Delhi-110007 (India>Fax : (+ 91) 98-1072-8438

A new protocol for the N-arylation of aryl halides with anilinesusing Cu nanoparticles in polyethylene glycol (PEG) as an effi-cient and reusable catalytic system has been developed. Thereaction did not require any cocatalyst. Various solvents werescreened, and PEG400 provided the best results. The studiesshowed that the mechanism of catalytic action is dependent

on the size of the nanoparticles. The Cu nanoparticles and PEGwere recyclable and retained their activity. This newly devel-oped protocol was also found to be suitable for the crosscoupling of N�H heterocycles with iodobenzene. The presentmethodology offers several advantages, such as excellentyields, short reaction times, and milder reaction conditions.

1312 � 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 2010, 2, 1312 – 1317

heterogeneous Cu nanoparticles catalyst and PEG solvent ischeap and recyclable with only a slight decrease of its activity.It is presumed that PEG works not only as the reactionmedium, but it also acts as a capping agent to stabilize theCu NP which conjugates with PEG to form a reactive species.[31]

Results and Discussion

Aniline (1.2 mmol) and iodobenzene (1 mmol) were used tooptimize the reaction condition with Cu nanoparticles ascatalyst. The reaction occurred to afford diphenyl amine in90 % yield when it was stirred for 5 h at 95 8C in the presenceof Cu nanoparticles (10 mol %) and K2CO3 (1.5 mmol) in PEG(Scheme 1). The structure was elucidated on the basis ofspectral data.

To optimize the reaction conditions, various parameters suchas the effect of different solvents and bases were studied onthe N-arylation. Among the solvents screened, dioxane, aceto-nitrile, toluene, DMF, PEG200, PEG400 and PEG600, we found thatPEG400 provided the best result. The reaction with K2CO3 wasmore effective in comparison to KOH (Table 1).

The concentration of catalyst plays a major role in thesynthesis of diphenyl amines derivatives through couplingreaction. By using the coupling of aniline and aryl iodide as amodel reaction and varying the concentration of Cu nano-particles, it was found that the optimum reaction rate andyield could be achieved at the catalyst concentration of10 mol % (Table 2).

Being a heterogeneous process, the experiment was carriedout to recycle the Cu NP/PEG400 system. After the completionof the reaction, the solution was cooled to room temperature.Because the Cu NP/PEG400 system is immiscible with diethylether and the product is soluble in ether, it was extracted withether. The insoluble Cu NP/PEG400 phase was reused for threecycles, and there was an approximately 5 % weight loss of PEGfrom cycle to cycle (Figure 1).

Scope of this novel protocol in N-arylation with otheramines was studied to determine the effect of substitutionpattern on the reaction yield. Substituted amines having elec-tron-donating groups such as 4-methoxy-, 2-methyl-, and 2-methoxyaniline (Table 3, entries 2, 6, 7) showed greater reactiv-ity in comparison to electron-withdrawing groups such as 4-chloro-, 4-bromo-, and 4-nitroaniline (Table 3, entries 3–5). Thereaction of aniline was also studied with substituted iodo-benzene. When iodobenzene was replaced by bromo- orchlorobenzene, the yields were comparatively low (Table 3).

We found that this newly developed protocol was alsosuitable for the cross-coupling of NH heterocycles with iodo-benzene, which gave the corresponding N-arylated products inexcellent yields in which imidazole derivatives required longerreaction times to complete the reaction (Table 4).

Scheme 1. N-Arylation of anilines and iodobenzene using Cu nanoparticles.

Table 1. Effect of solvents on the Cu NP catalyzed cross-coupling ofaniline with aryl iodide.

Entry Solvent/base T [8C] t [h] Yield [%][b]

1 dioxane/K2CO3 100 5 02 acetonitrile/

K2CO3100 5 0

3 toluene/K2CO3 100 5 254 DMF/K2CO3 100 5 105 PEG200/K2CO3 100 5 866 PEG400/K2CO3 95 5 907 PEG600/K2CO3 100 5 908 PEG400/K2CO3 RT 10 09 PEG400/KOH RT 10 010 PEG400/KOH 110 5 45

[a] Reaction conditions: aniline (1.2 mmol), aryl iodides (1 mmol), base(1.5 mmol), Cu NP (18�2) nm (10 mol %), solvent (2 mL); T = 95 8C;[b] yields of isolated product.

Table 2. Optimization of Cu nanoparticles for N-arylation.[a]

Entry Cu NP (18�2 nm) [mol %] t [h] Yield [%][b]

1 5 5 702 10 5 903 15 5 854 20 5 21

[a] Reaction conditions: aniline (1.2 mmol), aryl iodides (1 mmol), K2CO3

(1.5 mmol), Cu NP (18�2) nm (5–20 mol %), PEG400 (2 mL); T = 95 8C;[b] yields of isolated product.

Figure 1. Recycling of Cu NP/PEG400 catalytic system (Table 3, entry 1).

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Cu Nanoparticles in PEG

Effect of particle size on the catalytic efficiency

The size of the Cu nanoparticles plays an important role interms of yields and reaction times. Changing the size ofparticles resulted in a drop in catalytic activity. Thus studiesshow that the mechanism of catalytic action is dependent onthe nanoparticles size (Table 5).

The maximum reaction rate was obtained for an averageparticle size of about 20 nm in diameter. With a decrease inparticle size, a trend of decreasing reaction rate has beenfound for particles with a diameter of less than 20 nm, whereasthose above this diameter shows a steady decline of reactionrate with increasing size. It has been postulated that in thecase of particles with an average size less than 20 nm, a down-ward shift of the Fermi level takes place, with a consequentincrease of band gap energy.[11, 32-35] As a result, the particles re-quire more energy to pump electrons to the adsorbed ions forthe electron transfer reaction. This leads to a reduction in reac-tion rate when catalyzed by smaller particles. On the otherhand, for nanoparticles >20 nm in diameter, the change ofFermi level is not appreciable. As these particles exhibit less

surface area for adsorption with increased particle size, adecrease in catalytic efficiency results.

Conclusions

In conclusion, we have developed a mild and efficient methodfor amination using Cu nanoparticles in PEG as environmental-ly benign solvent. The catalyst and solvent were recovered andthey retained their activity. In comparison to other transitionmetal catalyst systems, this protocol is simple and avoids theuse of expensive metal catalysts or additives. To the best ofour knowledge, this is the first catalytic system for the N-aryla-tion of NH-containing substrates. Further studies to elucidatethe mechanism of this catalytic system and to extend thisprocess to other reactions is ongoing in our laboratory.

Table 3. Cross-coupling reaction of substituted anilines with aryl halidesusing Cu nanoparticles as catalyst.[a]

Entry R X t [h] Product Yield [%][b]

1 C6H5 I 5 90

2 4-OCH3C6H4 I 5.2 93

3 4-ClC6H4 I 6 91

4 4-BrC6H4 I 5.5 82

5 4-NO2C6H4 I 12 70

6 2-CH3C6H4 I 3.5 94

7 2-OCH3C6H4 I 4 95

8 C6H5 Br 12 81

9 4-OCH3C6H4 Br 10 90

10 C6H5 Cl 10 60

[a] Reaction conditions: aniline (1.2 mmol), aryl iodides (1 mmol), K2CO3

(1.5 mmol), Cu NP (18�2) nm (10 mol %), PEG400 (2 mL); T = 95 8C;[b] yields of isolated product.

Table 4. Reaction of NH heterocycles with iodobenzene.[a]

Entry Substrate Product t [h] Yield [%][b]

1 6 89

2 8 91

3 18 69

4 18 70

5 26 95

[a] Reaction conditions: NH heterocycles (1.2 mmol), aryl iodides(1 mmol), K2CO3 (1.5 mmol), Cu NP (18�2) nm (10 mol %), PEG400 (2 mL);T = 95 8C; [b] yields of isolated product.

Table 5. Size screening of Cu nanoparticles in cross-coupling reactions ofaniline and aryl iodide.[a]

Entry Particle size (�2 nm) t [h] Yield [%][b]

1 10 5 882 20 3 943 30 3.5 904 50 6 70

[a] Reaction conditions: aniline (1.2 mmol), aryl iodides (1 mmol), K2CO3

(1.5 mmol), Cu NP (18�2) nm (10 mol %), PEG400 (2 mL); T = 95 8C;[b] yields of isolated product.

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M. Kidwai et al.

Experimental Section

The materials were purchased from Sigma–Aldrich and Merck andwere used without any further purification. All reactions and purityof diphenyl amines were monitored by thin layer chromatography(TLC) using aluminum plates coated with silica gel (Merck) usinghexane/ethylacetate (80:20) as an eluent. The isolated productswere further purified by column chromatography using silica gel G(particle size 10–40 microns, 300 mesh) purchased from Spectro-chem Pvt. Ltd. Mumbai, India. Melting points were determined onBuchi 530. 1H NMR spectra were recorded on a Bruker AvanceSpectrospin 300 (300 MHz). All NMR samples were run in CDCl3

and chemical shifts were expressed as ppm relative to internalMe4Si. The size and morphology of Cu nanoparticles were charac-terized by using a transmission electron microscope (TEM, FEIPhilips Morgagni 268D model, ac voltage of 100 kV with a magnifi-cation of up to 2, 80 000 � ) and a quasi elastic light scatteringinstrument (QELS, photocor-FC, Model-1135P). The metallic natureof the particles was confirmed by using a UV spectrophotometer(Shimadzu).

Preparation of Cu nanoparticles

A chemical method involving reduction of Cu2+ ions to Cu0 in areverse micellar system was employed to prepare the coppernanoparticles (Scheme 2).[36–38] Poly(oxyethylene) (tetra methyl

butyl) phenyl ether, commercially known as Triton X-100 (TX-100)was used as the surfactant with cyclohexane as the solvent contin-uous phase, hexanol as cosurfactant and aqueous solution of saltsas dispersed phase (water core in which particle formation occurs).The reverse micelles were prepared by dissolving TX-100 in cyclo-hexane (usually 0.08–0.15 m of TX-100 solution). A typical prepara-tive method is as follows: To a set volume of 100 mL (0.1 m TX-100solutions in cyclohexane), CuSO4 aqueous solution (900 mL, 2 % w/v) and hexanol (quantity substituent, q.s.) were added to preparean optically clear reverse micellar solution (RM-1). To another solu-tion of 0.1 m TX-100 in cyclohexane (100 mL), N2H2 solution (5 %aqueous solution) and hexanol (q.s.) were added to obtain RM-2.To the prepared reverse micellar solution of CuSO4 aqueous solu-tion (2 % w/v) (RM-1), another reverse micellar N2H2 solution (5 %aqueous solution) (RM-2) was added dropwise with constant stir-ring under the nitrogen atmosphere. In the presence of nitrogenatmosphere, the resulting solution was allowed to stir for threehours to complete the Ostwald ripening (particle growth). Thecopper nanoparticles were extracted by adding absolute ethanolto the reverse micellar solution containing Cu nanoparticles fol-lowed by centrifugation at 3000–4000 rpm for 10 min. By varying

the water content parameter W0 (defined as the molar ratio ofmolar concentration of water to surfactant concentration, W0 =

[H2O]/[surfactant] , the size of the nanoparticles could be con-trolled. The sizes of the Cu nanoparticles prepared at W0 = 5 wereconfirmed as 14–18 nm through quasi elastic light scattering(QELS) data (Figure 2 a) and TEM measurements (Figure 2 b). The

Cu nanoparticles prepared were round in shape and brown incolor (colloidal state). TEM photographs (Figure 2 b) confirmed thesizes of copper nanoparticles used in the experiment. The metallicnature of the Cu0 nanoparticles was confirmed by a characteristicUV absorption of particles dispersed in cyclohexane (Figure 3).

General procedure for the synthesis of diphenyl amines

In a 50 mL round bottom flask, substituted anilines (1.2 mmol), arylhalides (1 mmol), and K2CO3 (1.5 mmol) in PEG (2 mL) were stirredunder a nitrogen atmosphere and Cu nanoparticles (10 mol % 18�

Scheme 2. Preparative procedure of Cu nanoparticles.

Figure 2. a) QELS data of Cu nanoparticles : Plot of population distribution inpercentile versus size distribution in nanometers; b) TEM image of Cu nano-particles.

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Cu Nanoparticles in PEG

2 nm) were added. The reaction mixture was allowed to be stirredat 95 8C for the appropriate time (Table 3). The extent of reactionwas monitored using TLC. After completion of the reaction, themixture was cooled and extracted with diethyl ether and the etherlayer was washed with brine solution, and then dried with anhy-drous sodium sulfate. Cu NP/PEG400 system being insoluble in etherwas recovered. The solvent was removed in vacuo, the crude reac-tion mixture was purified by silica gel column chromatographyusing 10 % ethyl acetate and 90 % petroleum ether as an eluent toyield the diphenyl amines. The recovered Cu NP/PEG400 catalyticsystem can be reused for consecutive runs. The structures of allthe products were unambiguously established on the basis of theirspectral analysis (1H NMR and 13C NMR spectral data). All theproducts are known compounds; those synthesized by novelroutes were elucidated by comparison with existing literature.

N-phenylaniline (Table 3, entry 1): Yellow solid, m.p. 52–53 8C.1H NMR (300 MHz, CDCl3): d= 7.54–7.50 (m, 4 H), 7.29–7.26 (d, J =8.7 Hz, 4 H), 6.91–6.82 (m, 2 H), 5.49 ppm (s, 1 H). 13CNMR (100 MHz,CDCl3): d= 118.04, 121.24, 129.54, 143.28 ppm.

N-(p-methoxyphenyl)aniline (Table 3, entry 2): Pale yellow solid,m.p. 103 8C, 1H NMR (300 MHz, CDCl3): d= 7.85–7.82 (d, J = 7.5 Hz,2 H), 7.48–7.36 (m, 5 H), 6.81–6.63 (m, 5 H), 4.30 (s, 1 H), 3.41 ppm (s,3 H). 13C NMR (100 MHz, CDCl3): d= 151.45, 146.32, 132.28, 129.10,123.41, 119.10, 52.23 ppm.

N-(p-chlorophenyl)aniline (Table 3, entry 3): Pale yellow solid,m.p. 71–72 8C; 1H NMR (300 MHz, CDCl3): d= 7.70–7.67 (d, 7.95 Hz,2 H), 7.40–7.38 (t, J = 7.68 Hz, 2 H), 7.11–7.05 (m, 3 H), 6.59–6.57 (d,J = 8.59 Hz, 2 H), 5.58 ppm (s, 1 H). 13C NMR (100 MHz, CDCl3): d=146.55, 141.24, 131.76, 122.83, 120.11, 116.40 ppm.

N-(p-Bromophenyl)aniline (Table 3, entry 4): Light yellow solid,m.p. 86 8C. 1H NMR (300 MHz, CDCl3): d= 7.72–7.69 (d, 7.94 Hz, 2 H),7.36–7.31 (t, J = 8.60 Hz, 2 H), 7.06–7.01 (m, 3 H), 6.92–6.88 (d, J =8.6 Hz, 2 H), 5.67 ppm (s, 1 H), 13C NMR (100 MHz, CDCl3): d=147.28, 143.43, 129.83, 129.46, 127.04, 118.21, 114.32 ppm.

N-(p-Nitrophenyl)aniline (Table 3, entry 5): Yellow solid, m.p. 130 8C;1H NMR (300 MHz, CDCl3): d= 8.08–8.05 (d, J = 9.0 Hz, 2 H), 7.26–7.23 (t, J = 8.25 Hz, 2 H), 7.20–7.12 (m, 3 H), 6.64–6.61 (d, J = 8.79 Hz,2 H), 4.40 ppm (s, 1 H). 13C NMR (100 MHz, CDCl3): d= 150.24,138.45, 137.12, 128.27, 127.56, 124.71, 123.42, 115.0 ppm.

N-(2-methylphenyl)aniline (Table 3, entry 6): Brownish solid,m.p. 40 8C; 1H NMR (300 MHz, CDCl3): d= 7.65–7.58 (m, 5 H), 7.28–

7.23 (t, J = 7.95 Hz, 1 H), 6.98–6.93 (m, 3 H), 4.26 (s, 1 H), 2.38 ppm(s, 3 H). 13C NMR (100 MHz, CDCl3): d= 145.46, 142.79, 132.34,128.72, 127.46, 124.68, 120.34, 119.21, 117.48, 22.53 ppm.

N-(2-methoxyphenyl)aniline (Table 3, entry 7): Yellowish oil, 1H NMR(300 MHz, CDCl3): d= 7.38–7.32 (m, 3 H), 7.21–7.18 (m, 2 H), 7.07–7.04 (t, J = 8.2 Hz, CDCl3), 6.84–6.78 (m, 3 H), 4.32 (s, 1 H), 3.39 ppm(s, 3 H), 13C NMR (100 MHz, CDCl3): d= 147.73, 142.28, 132.36,129.12, 120.89, 118.20, 117.35, 115.26, 56.43 ppm.

N-phenylpyrrole: (Table 4, entry 1): Light yellow solid, m.p. 60–62 8C; 1H NMR (300 MHz, CDCl3): d= 7.86–7.83 (d, J = 8.6 Hz, 2 H),7.44–7.32 (m, 3 H), 7.21–7.18 (m, 2 H), 6.40–6.36 ppm (m, 2 H).13C NMR (100 MHz, CDCl3): d= 142.63, 130.42, 129.73, 127.64,125.74, 120.72, 118.46, 110.51 ppm.

N-phenylindole: (Table 4, entry 2): Colorless solid, m.p. 60–62 8C;1H NMR (300 MHz, CDCl3): d= 7.66–7.64 (d, J = 7.8 Hz, 1 H), 7.51–7.48 (m, 3 H), 7.36–7.34 (m, 2 H), 7.28–7.23 (m, 3 H), 6.78 ppm (s,1 H). 13C NMR (100 MHz, CDCl3): d= 139.85, 134.97, 129.67, 129.41,128.07, 127.43, 123.94, 121.30, 112.76, 105.23 ppm.

N-phenylimidazole: (Table 4, entry 3): Colorless solid, m.p. 60–62 8C;1H NMR (300 MHz, CDCl3): d= 7.85 (s, 1 H), 7.54–7.51 (m, 2 H), 7.32–7.30 (m, 3 H), 7.27 (s, 1 H), 7.18 ppm (s, 1 H). 13C NMR (100 MHz,CDCl3): d= 138.41, 135.76, 129.16, 128.16, 127.17, 120.66, 119.54,110.83 ppm.

N-(phenyl)-5-methyl-imidazole: (Table 4, entry 4): Yellowish oil,1H NMR (300 MHz, CDCl3): d= 7.42–7.36 (m, 5 H), 7.24–7.22 (m, 3 H),6.91 (s, 1 H), 6.84 ppm (s, 1 H). 13C NMR (100 MHz, CDCl3): d=128.93, 128.27, 126.32, 125.68, 119.86, 12.92 ppm.

N-(phenyl)-5-methyl-imidazole: (Table 4, entry 5): Pale yellow solid,m.p. 98 8C, 1H NMR (300 MHz, CDCl3): d= 8.09 (s, 1 H), 7.74–7.40 (m,6 H), 7.26–7.22 ppm (m, 2 H). 13C NMR (100 MHz, CDCl3): d= 146.36,132.28, 127.30, 124.30, 124.17, 122.33, 120.63, 112.46 ppm.

Acknowledgements

Neeraj Kumar Mishra, S. Bhardwaj, and Anwar Jahan thankC.S.I.R. and U.G.C. , New Delhi, India for grant of the Junior andSenior Research Fellowships.

Keywords: amines · copper · cross-couplings · heterogeneouscatalysis · nanoparticles

[1] A. F. Littke, G. C. Fu, Angew. Chem. 2002, 114, 4350 – 4386; Angew. Chem.Int. Ed. 2002, 41, 4176 – 4211.

[2] T. Gungor, A. Fouquet, J. M. Teulon, D. Provost, M. Cazes, A. Cloarec, J.Med. Chem. 1992, 35, 4455 – 4463.

[3] P. L�pez-Alvarado, C. AvendaÇo, J. C. Men�ndez, J. Org. Chem. 1996, 61,5865 – 5870.

[4] M. Negwar, in Organic-Chemical Drugs and their Synonyms : (An Inter-national Survey), 7th ed. , Akademic, Berlin, 1994.

[5] J. F. Hartwig, Angew. Chem. 1998, 110, 2154 – 2177; Angew. Chem. Int. Ed.Engl. 1998, 37, 2046 – 2067.

[6] J. P. Wolfe, S. Wagaw, J. F. Marcoux, S. L. Buchwald, Acc. Chem. Res.1998, 31, 805 – 818.

[7] W. C. Shakespeare, Tetrahedron Lett. 1999, 40, 2035 – 2038.[8] D. M. T. Chan, K. L. Monaco, R. P. Wang, M. P. Winters, Tetrahedron Lett.

1998, 39, 2933 – 2936.[9] D. A. Evans, J. L. Katz, T. R. West, Tetrahedron Lett. 1998, 39, 2937 – 2940.

[10] P. Y. S. Lam, C. G. Clark, S. Saubern, J. Adams, M. P. Winters, D. M. T.Chan, A. Combs, Tetrahedron Lett. 1998, 39, 2941 – 2944.

[11] M. Samim, N. K. Kaushik, A. Maitra, Bull. Mater. Sci. 2007, 30, 535 – 540.

Figure 3. UV spectrum for characterizing the metallic nature of the Cu nano-particles.

1316 www.chemcatchem.org � 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 2010, 2, 1312 – 1317

M. Kidwai et al.

[12] V. Engels, F. Benaskar, N. G. Patil, E. V. Rebrov, V. Hessel, L. A. Hulshof,D. A. Jefferson, A. J. M. Vekemans, S. Karwal, J. C. Schouten, A. E. H.Wheatley, Org. Process Res. Dev. 2010, 14, 644 – 649.

[13] B. C. Ranu, K. Chattopadhyay, L. Adak, A. Saha, S. Bhadra, R. Dey, D.Saha, Pure Appl. Chem. 2009, 81, 2337 – 2354.

[14] F. Ullmann, Ber. Dtsch. Chem. Ges. 1903, 36, 2382 – 2391.[15] For a review, see: J. Lindley, Tetrahedron 1984, 40, 1433 – 1456.[16] M. L. Kantam, B. V. Prakash, Ch. V. Reddy, J. Mol. Catal. A 2005, 241,

162 – 165.[17] J. Chen, S. K. Spear, J. G. Huddleston, R. D. Rogers, Green Chem. 2005, 7,

64 – 82.[18] C. M. Starks, C. L. Liotta, M. Halpern in Phase-Transfer Catalysis : Funda-

mentals, Applications and Industrial Perspectives, Chapman & Hall, NY,1994, p. 158.

[19] J. G. Huddleston, H. D. Willauer, S. T. Griffin, R. D. Rogers, Ind. Eng. Chem.Res. 1999, 38, 2523 – 2539.

[20] R. Hatti-Kaul, Mol. Biotechnol. 2001, 19, 269 – 277.[21] C. Luo, Y. Zhang, Y. Wang, J. Mol. Catal. A 2005, 229, 7 – 12.[22] M. Kidwai, D. Bhatnagar, N. K. Mishra, V. Bansal, Catal. Commun. 2008, 9,

2547 – 2549.[23] S. L. Jain, S. Singhal, B. Sain, Green Chem. 2007, 9, 740 – 741.[24] M. T. Reetz, R. Breinbauer, K. Wanninger, Tetrahedron Lett. 1996, 37,

4499 – 4502.[25] M. T. Reetz, S. A. Quaiser, C. Merk, Chem. Ber. 1996, 129, 741 – 743.[26] M. Moreno-MaÇas, R. Pleixats, S. Villarroya, Organometallics 2001, 20,

4524 – 4528.

[27] J. Dupont, G. S. Fonseca, A. P. Umpierre, P. F. P. Fichtner, S. R. Teixeira, J.Am. Chem. Soc. 2002, 124, 4228 – 4229.

[28] M. B. Thathagar, J. Beckers, G. Rothenberg, J. Am. Chem. Soc. 2002, 124,11858 – 11859.

[29] M. Kidwai, N. K. Mishra, V. Bansal, A. Kumar, S. Mozumdar, TetrahedronLett. 2009, 50, 1355 – 1358.

[30] M. Kidwai, V. Bansal, N. K. Mishra, A. Kumar, S. Mozumdar, Synlett 2007,1581 – 1584.

[31] S. Jammi, S. Krishnamoorthy, P. Saha, D. S. Kundu, S. Sakthivel, A. Ali, R.Paul, T. Punniyamurthy, Synlett 2009, 3323 – 3327.

[32] A. K. Verma, R. Kumar, P. Chaudhary, A. Saxena, R. Shankar, S. Mozumdar,R. Chandra, Tetrahedron Lett. 2005, 46, 5229 – 5232.

[33] A. Kumar, S. Kumar, A. Saxena, A. De, S. Mozumdar, Catal. Commun.2008, 9, 778 – 784.

[34] R. K. Sharma, P. Sharma, A. N. Maitra, J. Colloid Interface Sci. 2003, 265,134 – 140.

[35] P. Sharma, S. Brown, G. Walter, S. Santra, B. Moudgil, Adv. Colloid Inter-face Sci. 2006, 123–126, 471 – 485.

[36] I. Lisiecki, M. P. Pileni, J. Am. Chem. Soc. 1993, 115, 3887 – 3896.[37] A. Saxena, A. Kumar, S. Mozumdar, Appl. Catal. A 2007, 317, 210 – 215.[38] J. Mao, J. Guo, F. Fang, S.-J. Ji, Tetrahedron 2008, 64, 3905 – 3911.

Received: March 9, 2010Revised: April 20, 2010Published online on July 21, 2010

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Cu Nanoparticles in PEG