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Palladium-Catalyzed Synthesis ofSymmetrical Biaryls Under MicrowaveIrradiation and Conventional HeatingAbdol Reza Hajipour a b & Fatemeh Rafiee aa Pharmaceutical Research Laboratory, Department of Chemistry,Isfahan University of Technology, Isfahan, Iranb Department of Pharmacology, University of Wisconsin, MedicalSchool, Madison, Wisconsin, USAAccepted author version posted online: 05 Jun 2012.Version ofrecord first published: 21 Feb 2013.

To cite this article: Abdol Reza Hajipour & Fatemeh Rafiee (2013): Palladium-Catalyzed Synthesisof Symmetrical Biaryls Under Microwave Irradiation and Conventional Heating, SyntheticCommunications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,43:9, 1314-1327

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PALLADIUM-CATALYZED SYNTHESISOF SYMMETRICAL BIARYLS UNDER MICROWAVEIRRADIATION AND CONVENTIONAL HEATING

Abdol Reza Hajipour1,2 and Fatemeh Rafiee11Pharmaceutical Research Laboratory, Department of Chemistry,Isfahan University of Technology, Isfahan, Iran2Department of Pharmacology, University of Wisconsin, Medical School,Madison, Wisconsin, USA

GRAPHICAL ABSTRACT

Abstract The activity of the [PdfC6H4(CH2N(CH2Ph)2)g(l-Br)]2 complex was investi-

gated in the synthesis of symmetrical biaryls under both conventional and microwave

irradiation conditions, and their results were compared. This complex is efficient, stable,

and not sensitive to air or moisture and is a catalyst for the homo-coupling reaction of aryl

iodides, bromides, and even chlorides. The products were produced in excellent yields in short

reaction times using a catalytic amount of [PdfC6H4(CH2N(CH2Ph)2)(l-Br)]2 complex

in N-methylpyrolidine (NMP) at 130 �C. In comparison to conventional heating conditions,

the reactions under microwave irradiation gave better yields in shorter reaction times.

Keywords Biaryls; cyclopalladated catalyst; homo-coupling reaction; tribenzylamine

INTRODUCTION

Because of the excellent physical and chemical properties of biaryls, they are ofgreat interest for the synthesis of biologically active compounds;[1] natural productsincluding alkaloids, coumarins, polyketides, and terpenes;[2] supramolecular com-pounds[3] or receptor macrocyclic molecules;[4] conductive materials;[5] and asymmet-ric catalysts.[6]

Received September 20, 2011.

Address correspondence to Abdol Reza Hajipour, Pharmaceutical Research Laboratory,

Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran. E-mail: haji@

cc.iut.ac.ir

Synthetic Communications1, 43: 1314–1327, 2013

Copyright # Taylor & Francis Group, LLC

ISSN: 0039-7911 print=1532-2432 online

DOI: 10.1080/00397911.2011.632830

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Transition metal–catalyzed homo-coupling of aryl halides is a very efficientcatalytic process for biaryls synthesis. Palladium,[7,8] nickel,[9] barium,[10] indium,[11]

copper, and rhodium[12] have been used in these reactions. The most convenientmethod for the synthesis of symmetrical biaryls is a reductive homo-coupling of arylhalides by the Ullmann reaction,[13] which requires harsh conditions such as equimo-lar amounts of copper, high temperature, and strong bases. The symmetrical biarylsalso synthesized by oxidative coupling of aryl boronic acid,[14] aryl zinc,[15] aryl stan-nanes,[16] and aryl mesylates.[17] Most researchers have put forth considerable effortto develop milder reaction conditions using new catalysts and reaction systems. Todevelop catalysts that can operate at low metal loading and mild reaction, complexa-tion of Pd with phosphines,[18–20] N-heterocyclic carbene (NHCs) complexes,[21] andpalladacycles has been considered. Among the proper methods, the palladacycle cat-alysts are the most important classes of catalysts because they are very efficient withlow concentration in organic synthesis, material science, biologically active com-pounds, and macromolecular chemistry.[22,23]

High-speed synthesis with microwaves has attracted attention in recent years.Homogeneous transition metal–catalyzed reactions are some of the most importantand well-studied reaction types in microwave-assisted organic and inorganic syn-thesis. The use of microwave irradiation in transition metal–catalyzed reactionshas assumed great importance because of the reduction of the reaction times, pro-ducing good yields and greater selectivity, the decrease of discarded by-productsfrom thermal side reactions, and increased lifetime of the catalyst.[24,25]

In continuation of our recent investigations on the synthesis of the palladacyclecatalysts and their application in microwave-assisted cross-coupling reactions,[26] wenow report the extension of a [PdfC6H4(CH2N(CH2Ph)2)(m-Br)]2 homogeneouscomplex, as a thermally stable and oxygen-insensitive catalyst for homo-couplingreaction of various aryl halides under conventional and microwave irradiation.

RESULTS AND DISCUSSION

Dimeric orthopalladate complex [PdfC6H4(CH2N(CH2Ph)2)g(m-Br)]2 (A)waspre-pared by treatment of tribenzylaminewith an equimolar amount of palladium(II) acetatein acetonitrile at 80 �Cas a binuclear complex. The reaction of this complexwithNaBr inacetone gave dimeric orthopalladate complex [PdfC6H4(CH2N(CH2Ph)2)g(m-Br)]2.[27]We have recently applied this complex in the Heck cross-coupling reaction.[28] Inthis report, efficiency of this catalyst was investigated in homo-coupling reaction ofvarious aryl halides under both traditional and microwave irradiation conditions(Scheme 1).

To find the best experimental conditions, the homo-coupling reaction of4-iodoanisole as the test substrate carried out using palladacycle A as the catalystin various solvents and organic and inorganic bases under conventional heating,as shown in Table 1.

As demonstrated in Table 1 (entry 2), K2CO3 as base and N-methyl-2-pyrrolidone (NMP) as solvent gave the best results. The other bases such as Cs2CO3,Na2CO3, NaOAc, and NEt3 were less effective. Potassium carbonate as a cocatalystfacilitates the reduction of palladium(II) species and has a positive effect on the reac-tion.[29] Various catalyst concentrations were also tested and 0.5mmol% (Table 2,

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entry 6) gave the best result. As this catalyst is not sensitive to oxygen, the reactionswere carried out under an air atmosphere.

The best conditions were applied in homo-coupling reaction of various arylhalides under conventional (Table 3) and microwave irradiation (Table 4).

As demonstrated in Tables 3 and 4, this catalytic system can be used forhomo-coupling reactions of different types of aryl iodides, bromides, andless-reactive aryl chlorides. The ideal substrates for coupling reactions are aryl chlor-ides, because they tend to be cheaper and more widely available than their bromideor iodide counterparts. Because of the high C-Cl bond strength compared with C-Brand C-I bonds, required times for conversion of aryl chlorides to biaryls are longerunder both reaction conditions (Tables 3 and 4, entries 18–20). We also examined the

Scheme 1. Homo-coupling reaction of aryl halides by using palladacycle catalyst A.

Table 1. Effect of various reaction conditions on homo-coupling of aryl halides under conventional

heatinga

Entry Base Solvent Time (min) Conversion (%)

1 K2CO3 DMF 80 90

2 K2CO3 NMP 60 100

3 Cs2CO3 NMP 80 70

4 Et3N NMP 80 Trace

5 Na2CO3 NMP 80 60

6 NaOAc NMP 80 80

7 K2CO3 DMAc 80 70

8 K2CO3 Toluene 80 15

9 K2CO3 DMSO 80 50

aReaction conditions: 4-iodoanisole (1mmol), base (1mmol), solvent (2ml), and palladacycle A

(0.3mmol%).

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electronic and steric effects on the yields of the reactions. Both electron-withdrawingand electron-donating aryl halides produced homo-coupling products efficiently.The steric hindrance of the procedure was examined using 2-, 3-, and 4-bromoaceto-phenone as hindered substituted aryls (Table 3 and 4, entries 9–11). Increasing thehindrance in the vicinity of a leaving group can cause a decrease in the reaction con-version. The chemoselectivity of the procedure was examined using 2-, 3-, and4-chlorobromobenzene. In these reactions, Br acted as a better leaving group(Tables 3 and 4, entries 12–14). The experimental conditions are identical to all sub-strates so it is possible to judge the reactivity of different substrates. Aryl chloridesand hindered substituted aryls show lower reactivity in coupling reactions. For thesesubstrates the homo-coupling reaction was run in a specific time to complete thesereactions. Longer times and greater load of catalyst are required.

A mechanistic description of the homo-coupling reaction is presented inScheme 2. Initially, Pd(II) pre-catalyst converts to Pd(0),[30] followed by the oxidat-ive addition of aryl halide to Pd(0) to form aryl palladium(II) intermediate 1. Anexchange between two molecules of intermediate 1 produced compounds 2 and 3.Finally, reductive elimination of intermediate 2 caused the desired coupling pro-ducts, and the Pd(0) formed in the main catalytic cycle. To evaluate the proposedmechanism of a catalytic system, we carried out the mercury drop test. In the pres-ence of a heterogeneous catalyst, mercury leads to the amalgamation of the surfaceof catalyst. In contrast, Hg(0) cannot have a poisoning effect on homogeneous pal-ladium complexes, where the Pd(II) metal center is tightly bound to the ligand. Whena drop of Hg(0) was added to the reaction mixture under this condition and is heatedin an oil bath, no biaryl product is obtained and no catalytic activity was observedfor the catalyst. The data obtained can be rationalized as a Pd(0)=Pd(II) cycle.

The results summarized in Table 4 showed that the use of homogenous metalcatalysts in conjunction with microwave irradiation in comparison to conventionalheating conditions led to dramatically reduced reaction times and greater yields.The dramatic rate enhancement is due to the rapid and uniform heating of the reac-tion mixture and increased catalyst lifetime by the elimination of wall effects in amicrowave versus oil-bath heating. Microwave irradiation raises the temperature

Table 2. Effect of catalyst concentration on homo-coupling reaction under conventional heatinga

Entry Catalyst (mol %) Time (min) Conversion (%)

1 None 90 0

2 0.05 90 10

3 0.1 90 25

4 0.2 55 92

5 0.4 50 95

aReaction conditions: 4-iodoanisole (1mmol), K2CO3 (1mmol), NMP (2ml), and palladacycle A,

130 �C.

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Table 3. Homo-coupling reaction of various aryl halides under the best obtained reaction conditions in

an oil batha

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

1 0.25 100 95

2 0.75 100 94

3 4 90 74

4 0.5 100 93

5 1.5 100 90

6 6 85 78

7 7 92 84

8 10 80 56

(Continued )

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Table 3. Continued

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

9 6 90 80

10 8 72 60

11 10 65 51

12 0.75 100 90

13 1.5 95 88

14 4 84 70

(Continued )

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Table 3. Continued

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

15 8 70 60

16 10 70 63

17 10 50 40

18 6 80 70

19 9 75 68

20 12 72 60

aReaction condition: aryl halide (1mmol), K2CO3 (1mmol), palladacycle catalyst A (0.5mmol%), NMP

(2ml), 130 �C.bIsolated yield.

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Table 4. Microwave-assisted homo-coupling reaction of various aryl halides under the best obtained reac-

tion conditionsa

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

1 2 100 100

2 6 100 100

3 14 95 88

4 3 100 96

5 8 100 97

6 35 100 90

7 15 100 93

8 30 92 80

(Continued )

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Table 4. Continued

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

9 20 98 90

10 30 85 76

11 45 75 64

12 3 100 100

13 5 100 96

14 12 95 86

15 18 100 90

(Continued )

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of the whole volume simultaneously (bulk heating) whereas in the oil-heated tube,the reaction mixture in contact with the vessel wall is heated first.[24]

EXPERIMENTAL

Reagents and Measurements

All melting points were taken on a Gallenkamp melting apparatus and areuncorrected.

1

H NMR spectra were recorded at 400MHz in CDCl3 solutions at

Table 4. Continued

Entry ArX Product

Time

(h)

Conversion

(%)

Yield

(%)b

16 30 95 82

17 40 65 55

18 25 96 90

19 25 96 89

20 25 88 78

aReaction condition: aryl halide (1mmol), K2CO3 (1mmol), palladacycle catalyst A (0.5mmol%), NMP

(2ml), 130 �C, 600W.bIsolated yield.

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room temperature (tetramethylsilane was used as an internal standard) on a BrukerAvance 500 instrument (Rheinstetten, Germany) and Varian 400 NMR. Fouriertransform–infrared (FT-IR) spectra were recorded on a spectrophotometer(Jasco-680, Japan). Spectra of solids were carried out using KBr pellets. Vibrationaltransition frequencies are reported as wave number (cm�1). We used the MilestoneMicrowave (Microwave Labstation MLS GmbH- ATC-FO 300) for synthesis.Furthermore, we used gas chromatography (BEIFIN 3420 gas chromatographequipped with a Varian CP SIL 5CB column 30m, 0.32mm, 0.25 mm) forexamination of reaction completion and yields. Palladium acetate, aryl halides,and all chemicals were purchased from Merck and Aldrich and were used asreceived.

General Procedure for Homo-Coupling Reaction of Aryl Halides

A mixture of the aryl halide (1mmol), K2CO3 (1mmol), and palladium preca-talyst A (0.5mmol %) was added to NMP (2mL) in a round-bottom flask equipped

Scheme 2. Proposed mechanism for homo-coupling reaction.

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with condenser and placed into theMilestone microwave or an oil bath. Initially usinga microwave power of 600W, the temperature was ramped from room temperature to130 �C, taking approximately 1min, and then held at this temperature until the reac-tion was completed. During this time, the power was modulated automatically tokeep the reaction mixture at 130 �C. The mixture was stirred continuously using anappropriate magnet during the reaction. The direct control of reaction mixture tem-perature was carried out with the IR sensors and software that enables online tem-perature–pressure control by regulation of microwave power output. During thistime, the power was modulated automatically to keep the reaction mixture at130 �C. The mixture was stirred continuously during the reaction and monitored byboth thin-layer chromatography and gas chromatography. After the reaction wascompleted, the mixture was cooled to room temperature and diluted with n-hexaneand water. The organic phase was dried overMgSO4, filtered, and concentrated underreduced pressure using a rotary evaporator. The residue was purified by silica-gel col-umn chromatography (n-hexane=EtOAc, 90:10) or recrystallization. The products inthis article have been reported previously and characterized by comparing their mp,IR, and 1H and 13C NMR spectra with those found in the literature.[20,26]

CONCLUSIONS

Use of dimeric orthopalladate complex [PdfC6H4(CH2N(CH2Ph)2)g(m-Br)]2 asan efficient and highly active, stable, and air- and moisture-insensitive catalyst forpromoting the homo-coupling reaction of various aryl halides was reported underboth conventional heating and microwave irradiation conditions. The combinationof dimeric complex as homogenous catalyst and microwave irradiation and alsoNMP as microwave-active polar solvent caused increase in the lifetime of thecatalyst, improved the yields of the reactions, and decreased the reaction times.

ACKNOWLEDGMENTS

We gratefully acknowledge the funding support received for this project fromthe Isfahan University of Technology (IUT), IR Iran, and Isfahan Science and Tech-nology Town (ISTT), Iran. Further financial support from the Center of Excellencein Sensor and Green Chemistry Research (IUT) is gratefully acknowledged.

REFERENCES

1. Bringmann, G.; Walter, R.; Weririch, R. The directed synthesis of biaryl compounds:Modern concepts and strategies. Angew. Chem., Int. Ed. Engl. 1990, 29, 971.

2. Lei, J. G.; Lin, G. Q. The first total synthesis of 4,40-biisofraxidin. Chin. J. Chem. 2002, 20,1263.

3. Suh, I. H.; Choi, S.; Lewis, D. E.; Jensen, W. P. Two related benzylcamphor dimmers.Acta Crystallogr. 1997, 53, 963.

4. Lehn, J. M. Supramolecular Chemistry, 1st ed.; VCH Verlasgesellschaft: Weinheim,

Germany, 1995.5. Chao, Y.; Weisman, G. R.; Sogah, G. D. Y.; Cram, D. J. Host–guest complexation, 21:

Catalysis and chiral recognition through designed complexation of transition states intransacylations of amino ester salts. J. Am. Chem. Soc. 1979, 101, 4948.

PALLADIUM-CATALYZED SYNTHESIS 1325

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by [

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8 Fe

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ry 2

013

6. Zhu, S. S.; Swager, T. M. Design of conducting redox polymers: A polythiophene-Ru(bipy)3 n

þ hybrid material. Adv. Mater. 1996, 8, 497.7. Lei, A.; Zhang, X. A novel palladium-catalyzed homocoupling reaction initiated by

transmetallation of palladium enolates. Tetrahedron Lett. 2002, 43, 2525.8. Seganish, W. M.; Mowery, M. E.; Riggleman, S.; DeShong, P. Palladium-catalyzed

homocoupling of aryl halides in the presence of fluoride. Tetrahedron 2005, 61, 2117.9. Tao, X. C.; Zhou, W.; Zhang, Y. P.; Dai, C. Y.; Shen, D.; Huang, M. Homocoupling of

aryl bromides catalyzed by nickel chloride in pyridine. Chin. J. Chem. 2006, 24, 939.10. Yanagisawa, A.; Hibino, H.; Habaue, S.; Hisada, Y.; Yamamoto, H. Highly selective

homocoupling reaction of allylic halides using barium metal. J. Org. Chem. 1992, 57, 6386.11. Ranu, B. C.; Dutta, P.; Sarkar, A. Indium-promoted reductive homocoupling of alkyl and

aryl halides. Tetrahedron Lett. 1998, 39, 9557.12. Posner, G. H. An Introduction to Synthesis Using Organocopper Reagents; John Wiley:

New York, 1980.13. Nelson, T. D.; Meyers, A. I. The asymmetric Ullmann reaction, 2: The synthesis of

enantiomerically pure C2-symmetric binaphthyls. J. Org. Chem. 1994, 59, 2655.14. Miyaura, N.; Suzuki, A. Palladium-catalyzed cross-coupling reactions of organoboron

compounds. Chem. Rev. 1995, 95, 2457.15. Negishi, E. Palladium- or nickel-catalyzed cross coupling: A new selective method for

carbon–carbon bond formation. Acc. Chem. Res. 1982, 15, 340.16. Farina, V. New perspectives in the cross-coupling reactions of organostannanes. Pure.

Appl. Chem. 1996, 68, 73.17. Percec, V.; Bae, J. Y.; Zhao, M.; Hill, D. H. Aryl mesylates in metal-catalyzed homocou-

pling and cross-coupling reactions, 1: Functional symmetrical biaryls from phenols vianickel-catalyzed homocoupling of their mesylates. J. Org. Chem. 1995, 60, 176.

18. Bedford, R. Palladacyclic catalysts in C-C and C-heteroatom bond-forming reactions.Chem. Commun. 2003, 9, 1787.

19. Qi, C.; Sun, X.; Lu, C.; Yang, J.; Du, Y.; Wu, H.; Zhang, X. M. Palladium-catalyzedreductive homocoupling reactions of aromatic halides in dimethyl sulfoxide (DMSO)solution. J. Organomet. Chem. 2009, 694, 2912.

20. Iranpoor, N.; Firouzabadi, H.; Azadi, R. Imidazolium-based phosphinite ionic liquid(IL-OPPh2) as Pd ligand and solvent for selective dehalogenation or homocoupling of arylhalides. J. Organomet. Chem. 2008, 693, 2469.

21. Navarro, O.; Marion, N.; Oonishi, Y.; Kelly III, R. A.; Nolan, S. P. Suzuki–Miyaura,a-ketone arylation and dehalogenation reactions catalyzed by a versatile N-heterocycliccarbene–palladacycle complex. J. Org. Chem. 2006, 71, 685.

22. Li, Q.; Nie, J.; Yang, F.; Zheng, R.; Zou, G.; Tang, J. Homocoupling of aryl iodides cat-alyzed by cyclopalladated complexes of tertiary arylamines. Chin. J. Chem. 2004, 22, 419.

23. Bedford, R. B.; Pilarski, L. T. Palladacyclic and platinacyclic catalysts for the allylation ofaldehydes. Tetrahedron Lett. 2008, 49, 4216.

24. Kappe, C. O. Controlled microwave heating in modern organic synthesis. Angew. Chem.Int. Ed. 2004, 43, 6250.

25. Singh, B. K.; Kaval, N.; Tomar, S.; Eycken, E. V.; Parmar, V. S. Transition metal–catalyzed carbon–carbon bond-formation Suzuki, Heck, and Sonogashira reactions usingmicrowave and microtechnology. Org. Process. Res. Dev. 2008, 12, 468.

26. Hajipour, A. R.; Karami, K.; Tavakoli, G. A comparative homocoupling reaction of arylhalides using monomeric orthopalladated complex of 4-methoxybenzoylmethylenetriphe-nylphosphorane under conventional and microwave irradiation conditions. Appl. Organo-met. Chem. 2011, 25, 567

27. Fuchita, Y.; Yoshinaga, K.; Hanaki, T.; Kawano, H.; Kinoshita-Nagaoka, J. Cyclopalla-dation of mono-, di-, and tribenzylamine by palladium(II) acetate: Influence of bulkiness

1326 A. R. HAJIPOUR AND F. RAFIEE

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rsity

] at

03:

14 2

8 Fe

brua

ry 2

013

around the nitrogen atom of benzylamine upon internal metallation. J. Organomet. Chem.1999, 580, 273.

28. Hajipour, A. R.; Rafiee, F. Application of dimeric cyclopalladated complex of tribenzyla-mine as an efficient catalyst in the Heck cross-coupling reaction. J. Organomet. Chem.2011, 696, 2669.

29. Schareina, T.; Zapf, A.; Beller, M. Improving palladium-catalyzed cyanation of arylhalides: Development of a state-of-the-art methodology using potassium hexacyanoferra-te(II) as cyanating agent. J. Organomet. Chem. 2004, 689, 4576.

30. Rosner, T.; Bars, J. L.; Pfaltz, A.; Blackmond, D. G. Kinetic studies of Heck couplingreactions using palladacycle catalysts: Experimental and kinetic modeling of the role ofdimer species. J. Am. Chem. Soc. 2001, 123, 1848.

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