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Journal of Organometallic Chemistry 696 (2011) 2559e2564

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Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

Selenoether ligand assisted Heck catalysis

Tapash Chakraborty a, Kriti Srivastava a, Harkesh B. Singh a,*, Ray J. Butcher b

aDepartment of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, IndiabDepartment of Chemistry, Howard University, Washington, DC 20059, USA

a r t i c l e i n f o

Article history:Received 9 January 2011Received in revised form18 March 2011Accepted 29 March 2011

Keywords:SelenoetherSelenideHeck reactionPalladium

* Corresponding author. Tel.: þ91 22 2576 7190; faE-mail addresses: tapashc@gmail.com (T. Chakra

(K. Srivastava), chhbsia@chem.iitb.ac.in (H.B. Singh).

0022-328X/$ e see front matter � 2011 Elsevier B.V.doi:10.1016/j.jorganchem.2011.03.047

a b s t r a c t

Selenoether ligands, 2,20-methylenebis(selanediyl)bis(2,1-phenylene)dimethanol (5), (2,20-(ethane-1,2-diylbis(selanediyl))bis(2,1-phenylene))dimethanol (6) and (2-(benzylselanyl)phenyl)methanol (7) havebeen synthesized by reducing di-o-formylphenyl diselenide and reacting the in situ generated selenolatewith dibromomethane, 1,2-dibromoethane and benzyl chloride, respectively. The ligands, bis(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenylselanyl)methane (8) and 1,2-bis(2-(4,4-dimethyl-4,5-dihy-drooxazol-2-yl)phenylselanyl)ethane (9) have been synthesized similarly from bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] diselenide using electrophiles dibromomethane and 1,2-dibromoethane, respectively.Activity of ligands 5e9 along with 2-(2-(benzylselanyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (10)and 1-(2-(benzylselanyl)phenyl)-N,N-dimethylmethanamine (11) were examined for the Heck reactionof aryl halides with olefins. Bidentate Se,N ligand 11 was found to be the best one in the series andconstitutes an efficient phosphine-free catalytic system with PdCl2. The catalytic system showedmoderate activity for the coupling of activated aryl chlorides in the presence of tetra-n-butyl ammoniumbromide (TBAB). Complexes [10-PdCl2] (12) and [11-PdCl2] (13) have shown marginally better activity incomparison to the in situ generated catalysts from PdCl2 and 10 and 11, respectively in the coupling of4-bromoacetophenone with n-butylacrylate. Ligand 9 and complex 13 have been characterized by singlecrystal X-ray diffraction analysis.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

Palladium catalyzed arylation or vinylation of olefins, known asthe Heck or the MizorokieHeck reaction, has evolved as a powerfultool in organic synthesis for CeC bond formation [1e14]. Aconventional Heck reaction involves coupling of an aryl halide anda terminal olefin bearing an electron withdrawing group catalyzedby 1e5 mol% of a palladium catalyst in presence of a phosphineligand and a suitable base [15e18]. However, the phosphine ligandsare generally expensive and air-sensitive. A number of phosphine-free catalysts have been employed in the Heck reaction. Amongthem the palladacycle catalysts [19] and N-heterocyclic carbene(NHC) ligands [20] have shown excellent activity. Other phosphine-free catalyst systems involve nitrogen, oxygen and sulfur ligatedcomplexes of palladium either as preformed catalysts or as in situcatalysts generated from an added ligand and a suitable palladiumprecursor. Although notmuch explored, these types of ligands havebeen shown to have interesting applications in the Heck reaction.

x: þ91 22 2576 7152.borty), akriti@chem.iitb.ac.in

All rights reserved.

Among the recent examples are amino acids [21], benzothiazoles[22], imidazolines [23], phenylureas [24], pyridylpyrazoles [25],and thiadiazolidine-1-oxides [26].

The use of selenium containing ligands in the Heck reaction ismuch rarer. Recently, the use of selenium ligated palladacycles andpalladium complexes in the Heck reaction has shown greatpotential [27]. These catalysts (1ae1c, Chart 1) are reported tooutperform the phosphorus and sulfur ligated catalysts includingthe best in the business like Herrmann palladacycle [28] and Mil-stein’s catalysts [29]. Recently, Singh and co-workers have usedpalladium complexes of SeNSe pincer ligands (2a, 2b, Chart 2) andselenoe and telluroether ligands containing benzotriazole moietyin the Heck and SuzukieMiyaura coupling reactions [30,31]. Morerecently, they have demonstrated that air and moisture stablepalladacycle generated from Se,N ligand in the SuzukieMiayuracoupling reactions show high catalytic activity [32]. We envisagedthat the use of bidentate or tetradentate, heteroleptic selenoetherligands incorporating nitrogen or oxygen can show interestingcatalytic properties in the Heck reaction. Herein, we report thesynthesis of selenoether ligands derived from di-o-formylphenyldiselenide [33] and bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] dis-elenide [34]. Utility of these ligands and other related ligands in theHeck reaction is described.

PdSe SePhPh PdSetBuCl

2Se SePd

Cl

Cl

OAc

1a 1b 1c

Chart 1. Selenium ligated catalysts.

O

Se )2

(i)

3

N

O

Se )2

4

(ii)/(iii)/(iv)

(i)(ii)/(iii)/(iv)

OH

Se R)n5, n = 2, R = -CH2-, (ii)6, n = 2, R = -CH2CH2-, (iii)7, n = 1, R = PhCH2-, (iv)

N

O

Se R)n8, n = 2, R = -CH2-, (ii)9, n = 2, R = -CH2CH2-, (iii)10, n = 1, R = PhCH2-, (iv)

NMe2

SeCH2Ph

(i)

11

NMe2

Se )2

(iv)

Scheme 1. (i) NaBH4, EtOH; (ii) CH2Br2, (iii) Br(CH2)2Br, (iv) PhCH2Cl.

Table 177

T. Chakraborty et al. / Journal of Organometallic Chemistry 696 (2011) 2559e25642560

2. Results and discussion

2.1. Synthesis of ligands

Selenoether ligands 5e9 were synthesized by reducing thediselenides viz. di-o-formylphenyl diselenide (3) [33] and bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] diselenide (4) [34] with NaBH4and reacting the resulting selenolates with various electrophilesshown in Scheme 1. The newly synthesized ligands were charac-terized by elemental analysis and NMR (1H, 13C and 77Se) spec-troscopy. The 77Se NMR spectroscopic data are given in thefollowing table (Table 1).

The eOH peak in the 1H NMR spectrum of 5 in CDCl3 appearedas a broad band at d 2.34 ppm. However, the eOH peak in the 1HNMR spectrum of 7 appeared as a sharp triplet at d 1.91 ppm inCDCl3. The reason may be the presence of strong intramolecularinteraction in this case. The chemical shifts in the 77Se NMR spectraof the ligands 5e7 [d 287 (5), 280 (6) and 320 ppm (7)] showed anupfield shift with respect to the parent diselenide 3 (d 468 ppm)[33]. Similarly, the 77Se chemical shift of the ligands 8 (d 325) and 9(350 ppm) showed an upfield shift with respect to the parent dis-elenide 4 (d 454 ppm) [34]. Ligands 10 and 11 were prepared byreducing the corresponding diselenides with NaBH4 and reactingthe resulting selenolates with PhCH2Cl. This represents a minormodification of the reported method for synthesis of the ligandswhere they were synthesized from the selenolates, generated insitu from the ortho-lithiated derivatives [35].

2.2. Synthesis of complexes

Palladium complexes 12 and 13 were synthesized as shown inScheme 2. The complexes were obtained by stirring the ligandsand metal precursor at room temperature. Any unreacted metalprecursor was separated from the synthesized complexes bycrystallizing from dichloromethane/hexane. The complexes werecharacterized by 1H and 77Se NMR spectroscopy and elementalanalysis. The methylene protons appeared as doublets at d 3.94and 4.20 ppm having coupling constant 12.0 Hz in the 1H NMRspectrum of 12 showing their diastereotopic nature. A similarsplitting pattern was observed in the 1H NMR spectrum of 13 (atd 3.06 and 4.58 with coupling constant 12.0 Hz). The 77Se NMRchemical shift of 12 appeared downfield by 54 ppm with respectto the free ligand 10 (d 421 ppm). However, the 77Se NMR signal of13 was upfield shifted by 78 ppmwith respect to the free ligand 11(d 321 ppm) [35].

NSeSe PhPh

Na[Pd(Cl)L][PdCl4][PdCl(L)]Cl.H2O

L =

2a 2b

Chart 2. SeNSe pincer ligands.

2.3. Crystallographic studies

2.3.1. Molecular structure of 9The molecular structure of 9 is shown in Fig. 1. The geometry

around the two selenium atoms is V-shaped. The intramolecularSe/N distance (2.830 Å) is less than the sum of their van derWaalsradii (3.40 Å) [36] showing significant secondary bonding interac-tion and is comparable with the Se/N distances observed in [2-(4,4-dimethyl-2-oxazolinyl)phenyl]benzyl selenide (2.798 Å) [35]and bis[2-(4,4-dimethyl-2- oxazolinyl)phenyl]diselenide (2.819 Å,2.705 Å) [34]. Seleniumecarbon(sp2) distance, SeeC1 [1.9141(18)Å] is shorter than the seleniumecarbon(sp3) distance, SeeC[1.9652(17) Å] and also shorter than the corresponding distances in[2-(4,4-dimethyl-2-oxazolinyl)phenyl]benzyl selenide [1.916(3) Å]and bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl]diselenide [1.946(9)Å, 1.940(9) Å]. Torsion angles, C1eSeeCeCi [172.50(15)�],CeSeeC1eC6 [174.96(13)�], CeSeeC1eC2 [e5.30(15)�] are close to180� or 0� showing the molecule to be almost planar.

2.3.2. Molecular structure of 13The molecular structure is depicted in Fig. 2. The geometry

around the palladium center is distorted square planar with thefour coordinations being defined by selenium, nitrogen and two cis-chloro donors. Trans-angle, Cl1ePdeSe [169.79(2) Å] deviates morethan the other angle, NePdeCl2 [176.53(7) Å] from linearity. Thebite angle, NePdeSe is 95.94(7) Å. The PdeCl2 bond distance[2.2898(8) Å], trans to nitrogen is slightly longer than the PdeCl1bond distance [2.2674(8) Å], trans to selenium. PdeN [2.065(2) Å]and PdeCl [2.2674(8) Å, 2.2898(8) Å] bond lengths are comparableto the corresponding distances in the similar structures [37e44].

Se NMR of ligands and complexes.

Compound 77Se NMR (d)

5 287a

6 280a

7 320a

8 325b

9 350b

12 367b

13 399b

a In CD3OD.b In CDCl3.

NMe2

Se

Ph

NMe2

Se

Ph

PdCl

Cl

Se

Ph

N

O

N

Se

Ph

PdCl

Cl

O

(i)

(i)

11

10

13

12

Scheme 2. (i) Pd(CH3CN)2Cl2, CH2Cl2.

Fig. 2. Molecular structure of complex 13; thermal ellipsoids are drawn at the 70%probability level; hydrogen atoms are removed for clarity. Significant bond lengths (Å)and bond angles (�): PdeSe 2.3166(6), PdeN 2.065(2), PdeCl1 2.2674(8), PdeCl22.2898(8), SeeC1 1.879(3), SeeC10 1.949(3) Å; NePdeCl1 93.19(7), NePdeCl2176.53(7), Cl1ePdeCl2 89.93(3), NePdeSe 95.94(7), Cl1ePdeSe 169.79(2), Cl2ePdeSe81.07(2), C1eSeeC10 99.28(13), C1eSeePd 109.07(9), C10eSeePd 101.25(9)� .

T. Chakraborty et al. / Journal of Organometallic Chemistry 696 (2011) 2559e2564 2561

PdeSe bond length [2.3166(6) Å] is shorter than that in the similarreported structures [38,41e43]. The selenium atom is in a nearpyramidal coordination with the bond angles around it being99.28(13)�, 101.25(9)� and 109.07(9)�.

2.4. Arylation of olefins: Heck coupling

2.4.1. Optimization of reaction conditionsTo start with, the reaction conditions for the Heck coupling were

optimized. In a typical Heck reaction of p-bromoacetophenonewithbutylacrylate in presence of K2CO3 as base catalyzed by PdCl2 at120 �C for 12 h (Eq. (1)), solvents N-methylpyrrolidone (NMP) andN,N-dimethylacetamide (DMA) were found to be of similar activityand more active than the other solvents like N,N-dimethylforma-mide (DMF), dioxane and toluene under ligand free condition(Table 2). The next step was to optimize the conditions to select thebest base from the commonly used ones, which was done usingNMP as the solvent and using the conditions as shown in Eq. (1).The results are summarized in the Table 3. Among the bases testedunder ligand free conditions NaOAc was found to be the mostsuitable.

2.4.2. Performance of the ligands 5e11 in the Heck reactionNext, we set out to evaluate the efficiency of the selenoether

ligands 5e11. The reactionswere performed under aerobic condition.

Fig. 1. Molecular structure of ligand 9; thermal ellipsoids are drawn at the 70%probability level; hydrogen atoms are removed for clarity. Selected bond lengths (Å)and bond angles and torsion angles(�): SeeC1 1.9141(18), SeeC 1.9652(17), Se/N2.830 Å; C1eSeeC 99.69(7), SeeCeCi 106.34(15), CeSe/N 174.69�; C1eSeeCeCi

172.51(17), CeSeeC1eC6 175.03(14)� .

The results are summarized in Table 4. Since the above reactionconditions were optimized under ligand free conditions, these werecompared with other reaction conditions including using differentsources of palladium in presence of the ligands 6, 7, 9e11which gavebest results under above conditions. The results are presented in thefollowing table (Table 5). Thus, on comparing Table 4 and Table 5, itwas seen that the combination of NMP as the solvent, NaOAc as thebase and PdCl2 as the source of palladium gives the best result. Also,ligands are necessary for thehigher activityof the catalyst since lesseryields were obtained under ligand-free conditions. The ligands con-taining benzyl groups i.e.10 (93%),11 (95%) and 7 (89%) gave the bestyields (Table 4: entry 6, 7 and 3). The bulkier ligands 6 and 9 wheretwo selenium atoms are separated by two carbons afforded betteryields compared to ligands 5 and 8 where two seleniums are sepa-rated by a methylene group. All of them were, however, inferiorcompared to the ligands 10 and 11. It was also observed that the Se,Nligands, 8e11weremore efficient compared to the Se,O ligands, 5e7.Among the Se,N ligands, Se,N(amine) ligand,11was found to bemoreactive compared toSe,N(imine) ligands,8,9and10. Althoughentry18and 22 in Table 5 shows same yield with PdCl2 and PdCl2(MeCN)2,solvents and bases used were different making the comparisonbetween PdCl2 and PdCl2(MeCN)2 in the two entries irrelevant. In thepresent study, under the optimized conditions,11þ PdCl2 was foundto constitute as the best catalytic system.

2.4.3. Evaluation of 11 þ PdCl2 in the Heck reactions of differentaryl bromides and chlorides with olefins

The results of coupling reactions using the catalytic system11 þ PdCl2 (1 mol%), in the Heck coupling of 4-substituted and

Table 2Optimization of solvents for the above reaction.a

Entry Solvent Yield (%)b

1 NMP 612 DMA 593 DMF 564 Dioxane 395 Toluene Trace

a Reaction condition: p-bromoacetophenone (1 mmol), butylacrylate (1.5 mmol),K2CO3 (2 mmol), PdCl2 (1 mol %), solvent (5 mL), 120 �C, 12 h.

b GC yield with respect to the aryl bromide.

Table 3Optimization of base.a

Entry Base Yield (%)b

1 K2CO3 612 Na2CO3 583 NaOAc 654 Et3N 455 Cs2CO3 506 K3PO4 47

a Reaction conditions: NMP (5 mL), bases (2 mmol) other conditions same as inTable 2.

b GC yield with respect to the aryl bromide.

Table 5Experimental conditions and yields of the coupling reactions.

Entry Ligand Solvent Base Pd source Yield (%)a

1 6 DMA Na2CO3 PdCl2 732 6 DMA K2CO3 PdCl2 753 6 DMF Na2CO3 PdCl2 704 6 DMF K2CO3 PdCl2 725 7 DMA Na2CO3 PdCl2 766 7 DMA K2CO3 PdCl2 817 7 DMF Na2CO3 PdCl2 688 7 DMF K2CO3 PdCl2 779 9 DMA Na2CO3 PdCl2 7510 9 DMA K2CO3 PdCl2 8111 9 DMF Na2CO3 PdCl2 7012 9 DMF K2CO3 PdCl2 7613 10 DMA Na2CO3 PdCl2 7914 10 DMA K2CO3 PdCl2 8715 10 DMF Na2CO3 PdCl2 8316 10 DMF K2CO3 PdCl2 8517 11 DMA Na2CO3 PdCl2 7918 11 DMA K2CO3 PdCl2 8819 11 DMF Na2CO3 PdCl2 8120 11 DMF K2CO3 PdCl2 7721 11 NMP NaOAc Pd(OAc)2 7222 11 NMP NaOAc Pd(CH3CN)2Cl2 8823 11 NMP NaOAc Pd(COD)Cl2 57

a GC yield with respect to aryl bromide. Reaction conditions same as in Table 4.

T. Chakraborty et al. / Journal of Organometallic Chemistry 696 (2011) 2559e25642562

unsubstituted aryl bromides and chlorides with olefins, n-butyla-crylateandstyreneare shown inTable6.Activatedarylbromidewithelectron withdrawing substituent gave good yield of the Heckproduct (entry 1 and 4). However, turnover numbers (TON) andturnover frequencies (TOF) were low because of comparativelyhigher catalyst concentration and longer reaction times. Non-activated, electron neutral aryl bromide, i.e., bromobenzene anddeactivated aryl bromide with electron donating substituent affor-ded yields in the range of 70e81% of the products (entry 2, 3, 5 and6). Aryl chlorides were unreactive under the reaction conditions(entry 7, 8 and 9). Use of tetra-n-butylammonium bromide (TBAB)afforded moderate yield of the product for the activated aryl chlo-rides (entry 7 and 8). Reducing the catalyst loading to 0.1 mol% didnot affect the yield of the reactions involving aryl bromide withn-butylacrylate significantly, although a longer reaction period of20 h was required increasing the TONs (entry 1, 2 and 3). Rate ofincrease of TOFs was comparatively low because of longer reactiontimes.

Additional investigations were carried out for the Heck couplingof 4-bromoacetophenone with n-butylacrylate in presence ofpalladium complexes 12 and 13 (entry 11). The isolated palladiumcomplexes 12 (95%) and 13 (98%) afforded better yields of coupledproducts compared to the in situ generated catalysts from theligands 10 (93%) and 11 (95%) [entry 11 of Table 6 vs entry 6 and 7 ofTable 4]. Presumably, the in situ catalyst did not form complexquantitatively and some unreacted PdCl2 was left resulting ina lower yield.

3. Conclusion

Ligands 5e11 constitute an effective phosphine-free catalyticsystem in the presence of PdCl2 for the Heck coupling of variousaryl bromides under aerobic conditions. Among them, the Se,Nbidentate ligands 8e11 were found to be more efficient ligands incomparison to the Se,O ligands 5e7. Ligands containing benzylgroup, 10, 11 and 7 were better in comparison to the rest of theligands. Bulkier ligands 6 and 9 were better in comparison to theirlighter counterparts 5 and 8 respectively. Bidentate Se,N ligand 11afforded the highest yield of the coupled product. The catalytic

Table 4Performance of the ligands in the Heck reaction.a

Entry Ligand Ligand:Pd Yield (%)b

1 5 2:1 702 6 2:1 853 7 1:1 894 8 2:1 795 9 2:1 876 10 1:1 937 11 1:1 95

a GC yield with respect to the aryl bromide.b p-bromoacetophenone (1 mmol), butylacrylate (1.5 mmol), NaOAc (2 mmol),

PdCl2 (1 mol%), NMP (5 mL), 120 �C, 12 h.

system showed moderate activity for the coupling of activated arylchlorides in presence of TBAB. Isolated complexes 12 and 13 haveshown marginally better activity in comparison to the in situcatalysts 10 þ PdCl2 and 11 þ PdCl2, respectively in the coupling of4-bromoacetophenone with n-butylacrylate.

4. Experimental

All the reactions were carried out under nitrogen or argon usingstandard vacuum-line techniques unless mentioned otherwise.Solvents were purified and dried by standard procedures and weredistilled prior to use. Ligands 3 [34] and 4 [35] were prepared by thereported procedures. Melting points were recorded on a VeegoVMP-I melting point apparatus in capillary tubes and were uncor-rected. Nuclear magnetic resonance spectra, 1H (400 MHz) and 13C(100.57 MHz) were recorded on a Varian Mercury plus 400 MHzspectrometer and a 77Se (57.22 MHz) on a Varian VXR 300S spec-trometer. Chemical shifts are cited with respect toMe4Si as internalstandard (1H, 13C) and Me2Se as external standard (77Se). Elementalanalyses were performed on a Carlo Erba elemental analyser model1106. Gas chromatographic analyses were carried out on a Shi-madzu 15A gas chromatograph. Temperature was programmed torun the analysis for 30 min reaching a maximum of 230 �C startingfrom 50 �C. Primary gas (nitrogen) flow rate was 40 mL/min. Yieldswere measured with respect to the conversion of the aryl halides.

4.1. Synthesis of ligands

4.1.1. General method for synthesis of ligandsTo a solution of the diselenide (2 mmol) in 50 mL of dry ethanol

was added NaBH4 in excess at 0 �C. After stirring for 30min the paleyellow color of the diselenide disappeared. To the colorless solutionof the resulting selenolate was added dibromomethane/benzylchloride (5 mL, excess) at 0 �C and stirred for 2 h. The reactionmixture was warmed to room temperature. It was then poured intobrine (50 mL) and extracted with 75 mL (3 � 25) of dichloro-methane. The organic extract was dried over anhydrous Na2SO4,concentrated under vacuum. The crude solid obtained was recrys-tallized from CHCl3/hexane (1:1) mixture to give white solid of theproduct.

Table 6Yields of the coupled products using 11 þ PdCl2.

Entry Aryl halide Olefin Yield (%)a TON TOF

1 4-Bromoacetophenone n-Butylacrylate 95/91b 95/910b 7.92/45.50b

2 Bromobenzene n-Butylacrylate 83/76b 83/760b 6.92/38.00b

3 4-Methoxybromobenzene n-Butylacrylate 72/66b 72/660b 3.60/33.00b

4 4-Bromoacetophenone Styrene 97 97 8.085 Bromobenzene Styrene 88 88 7.336 4-Methoxybromobenzene Styrene 76 76 6.337 4-Chloroacetophenone n-Butylacrylate Trace/45c 0/45c 0/3.758 4-Chloroacetophenone Styrene Trace/52c 0/52c 0/4.339 Chlorobenzene n-Butylacrylate Trace 0 010 4-Methoxychlorobenzene n-Butylacrylate Trace 0 011 4-Bromoacetophenone n-Butylacrylate 95d/98e 95d/98e 7.92d/8.17e

a Isolated yield.b In presence of 0.1 mol% of Pd and 20 h of reaction time.c In presence of 20 mol% TBAB at 140 �C.d In presence of 12.e In presence of 13.

T. Chakraborty et al. / Journal of Organometallic Chemistry 696 (2011) 2559e2564 2563

4.1.1.1. Synthesis of 5. Yield: 706 mg (91%), mp 182e184 �C. Anal.Calcd for C15H16O2Se2: C, 46.65; H, 4.18. Found: C, 46.93; H, 3.86. 1HNMR(CDCl3): d 2.34 (b, eOH, 2H), 4.21 (s, SeCH2Se, 2H), 4.69 (s,CH2OH,4H), 7.21e7.42 (m,2H), 7.56 (d, J¼1.2Hz,1H), 7.58 (d, 0.8Hz).13C NMR (CD3OD): 20.9 (SeCH2Se), 65.3(CH2OH), 128.8, 129.1, 129.3,132.3, 134.4, 143.9 (aromatic C). 77Se NMR (CD3OD): d 287.

4.1.1.2. Synthesis of 6. Yield: 627 mg (78%), mp 196e198 �C. Anal.Calcd for C16H18O2Se2: C, 48.01; H, 4.53; Found: C, 48.08; H, 4.08. 1HNMR (CD3OD): d 3.08 (s, SeCH2, 2H), 4.68 (s, CH2OH, 2H), 4.69 (s,CH2OH, 4H), 7.13e7.17 (dt, J ¼ 7.2 Hz, 1.6 Hz, 1H), 7.26e7.30 (dt,J ¼ 7.6 Hz, 1.2 Hz, 1H), 7.36e7.38 (dd, 8.0 Hz, 1.2 Hz), 7.44e7.47 (dd,7.6 Hz, 1.2 Hz). 13C NMR (CD3OD): 27.9 (SeCH2), 65.2 (CH2OH), 128.7,129.1,129.2,130.2,134.5,144.4 (aromaticC). 77SeNMR(CD3OD): d280.

4.1.1.3. Synthesis of 7. Yield: 1.05 g (95%), mp 160e162 �C. Anal.Calcd for C14H14OSe: C, 60.66; H, 5.09; Found: C, 60.40; H, 4.51. 1HNMR(CDCl3): d 1.91 (t, J¼ 6.4 Hz, eOH, 1H), 4.05 (s, SeCH2, 2H), 4.57(d, J ¼ 6.4 Hz, CH2OH, 2H), 7.10e7.12 (m, 2H), 7.14e7.31 (m, 5H),7.35e7.38 (dd, J ¼ 7.6 Hz, 1.6 Hz, 1H), 7.54e7.56 (dd, J ¼ 7.6 Hz,1.2 Hz, 1H). 13C NMR (CDCl3): 32.7 (SeCH2), 65.4 (CH2OH), 127.1,128.3,128.5,128.6,128.8,129.8,135.4,138.6,143.3 (aromatic C). 77SeNMR (CDCl3): d 320.

Table 7Crystal data and structure refinement for 9 and 13.

9 13

Empirical formula C24H28N2O2Se2 C16H19Cl2NPdSeFw 534.40 81.58Crystal system Monoclinic OrthorhombicSpace group C2/c Pna21a [Å] 26.8382(16) 12.070(3)b [Å] 9.0050(4) 23.358(5)c [Å] 9.8683 5.7323(12)a [�] 90 90b [�] 105.385 90g [�] 90 90V [Å3] 2299.5(2) 1616.1(6)Z 4 4Dcalcd. [mgm�3] 1.544 1.979Temp [K] 273(2) 123(2)q range [�] 4.72e32.74 3.11e28.29Abs. coeff. [mm�1] 3.239 3.723Final R(F) [I > 2s(I)]a 0.0294 0.0210wR(F2) indices [I > 2s(I)] 0.0434 0.0258Data/restraints/parameters 3800/0/138 3752/1/192Goodness of fit on F2 0.958 1.007

a Definitions: R(Fo) ¼ PjjFoj e jFcjj/PjFoj and wR(Fo2) ¼ {

P[w(Fo2 e Fc

2)]2/P

[w(Fc2)2]}1/2.

4.1.1.4. Synthesis of 8. Yield: 832 mg (80%), mp 210e212 �C. Anal.Calcd for C23H26N2O2Se2: C, 53.08; H, 5.04; N, 5.38 Found: C, 52.70;H, 4.76; N, 5.51. 1H NMR(CDCl3): d 1.39 (s, 12H), 4.00 (s, SeCH2, 2H),4.07 (s, CH2O, 4H), 7.19e7.23 (dt, J ¼ 8 Hz, 1.2 Hz, 1H), 7.36e7.40 (dt,J¼ 7.6 Hz,1.2 Hz,1H), 7.58 (d, J¼ 7.6 Hz,1H), 7.79e7.81 (dd, J¼ 8 Hz,1.2 Hz,1H). 13C NMR (CDCl3): 17.4 (CMe2), 28.8 (SeCH2), 68.7 (CMe2),78.9 (CH2O), 124.9, 126.9, 127.9, 129.9, 131.2, 137.3, (aromatic C),161.39 (C]N). 77Se NMR (CDCl3): d 325.

4.1.1.5. Synthesis of 9. Yield: 641 mg (61%), mp 218e220 �C. Anal.Calcd for C24H28N2O2Se2: C, 53.94;H, 5.28; N, 5.24 Found: C, 53.68; H,5.47;N,5.61.1HNMR(CDCl3):d1.43 (s,12H),3.19 (s, SeCH2, 4H),4.08(s,CH2O, 4H), 7.21 (t, J ¼ 7.2 Hz, 1H), 7.32 (t, J ¼ 7.2 Hz, 1H), 7.38 (t,J¼ 8.0 Hz, 1H), 7.79 (d, J¼ 8.0 Hz, 1H). 13C NMR (CDCl3): 24.8 (CMe2),28.8 (SeCH2), 68.8 (CMe2), 78.9 (CH2O),125.2,128.1,128.4,130.4,131.1,134.4, (aromatic C), 161.6 (C]N). 77Se NMR (CDCl3): d 350.

4.2. Synthesis of complexes

4.2.1. General method for synthesis of complexesTo a solution of 2-(4,4-dimethyl-2-oxazolinyl) phenyl benzyl-

selenide/N,N-dimethylaminobenzylselenide [35] (1 mmol) in20 mL of dry dichloromethane was added Pd(CH3CN)2Cl2 (259 mg,1 mmol) and stirred at room temperature for 2 h. The solution wasfiltered through a celite pad and concentrated to ca. 2 mL. It wasthen layered with 1 mL of hexane and kept at 0 �C overnight whenorange crystals of the title compound were obtained.

4.2.1.1. Synthesis of 12. Yield: 500 mg (96%), mp 225e227 �C. Anal.Calcd for C18H19Cl2NOPdSe: C, 41.45; H, 3.67; N, 2.69. Found: C,41.87; H, 3.49; N, 3.03. 1H NMR(CDCl3): d 1.83 (s, NMe2, 6H), 1.92(s,NMe2, 6H), 3.94 (d, J ¼ 12.0 Hz, SeCH2, 1H), 4.20 (d, J ¼ 12.0 Hz,SeCH2, 1H), 4.41e4.47 (m, CH2O, 2H), 6.95 (d, J ¼ 10.8 Hz, 2H),7.18e7.27 (m, 3H), 7.36 (d, J ¼ 8.0 Hz, 1H), 7.44e7.49 (m, 1H),7.61e7.65 (m, 1H), 7.88e7.89 (m, 1H). 77Se NMR (CDCl3): d 367.

4.2.1.2. Synthesis of 13. Yield: 430 mg (90%), mp 201e203 �C. Anal.Calcd for C16H19Cl2NPdSe: C, 39.90; H, 3.98; N, 2.91. Found: C, 40.13;H, 3.55; N, 3.20. 1H NMR(CDCl3): d 2.46e2.82 (2 broad bands, NMe2,12H), 3.06 (d, J¼ 12.0 Hz, CH2NMe2, 2H), 4.58 (d, J¼ 12.0 Hz, SeCH2,2H), 7.20e7.22 (m, 1H), 7.30e7.36 (m, 5H), 7.44e7.51 (m, 2H), 7.58(d, J ¼ 8.0 Hz, 1H). 77Se NMR (CDCl3): d 399.

4.3. General method for optimization of the catalytic reactioncondition using gas chromatography

A two-necked round-bottomed flask was charged with arylbromide (1 mmol), olefin (1.5 mmol), base (2 mmol), solvent (5 mL)

T. Chakraborty et al. / Journal of Organometallic Chemistry 696 (2011) 2559e25642564

and catalyst (1 mol%) and heated in a preheated oil bath fora specified time at the specified temperature. Then the reactionmixture was cooled to room temperature, filtered through a celitepad, washed with water and extracted with dichloromethane. Theorganic extract was dried over anhydrous Na2SO4 and filtered. Analiquot of 0.4 mL was taken into a microsyringe, injected in the gaschromatographic column and run for 30 min under presettemperature program. Yields were measured with respect to theconversion of the aryl halides.

4.4. General method for Heck coupling of aryl bromides andchlorides

A two-necked round-bottomed flask was charged with arylbromide/chloride (1 mmol), olefin (1.5 mmol), base (2 mmol),solvent (5mL)andcatalyst (LePd:1:1or1:2,1e0.1mol%) andheatedin a preheated oil bath for a specified time at specified temperature.Then the reaction mixture was worked up as above and purified bycolumn chromatography (silica: 60e120, hexane-ethyl acetate).

4.5. Crystal structure determination of 9 and 13

The diffraction measurements for 9 and 13 were performed atroom temperature and at 123(2) K on ‘Oxford Diffraction Gemini’(9) and ‘Bruker Apex 20 diffractometers (13) with graphite-monochromated Mo Ka radiation (l ¼ 0.71073 Ǻ). The data werecorrected for Lorentz, polarization and absorption effects. Thestructures were determined by routine heavy-atom methods usingSHELXS 97 [45] and Fourier methods and refined by full-matrixleast squares with the non-hydrogen atom anisotropic andhydrogen with fixed isotropic thermal parameters of 0.07 Ǻ2 bymeans of the SHELEXL 97 [46] program. The hydrogens werepartially located from difference electron-density maps, and therest were fixed at predetermined positions. Scattering factors werefrom common sources [47]. Some details of the data collection andrefinement are given in Table 7.

Acknowledgements

We are thankful to the Department of Science and Technology(DST), India for funding this work. Additional help from theSophisticated Analytical Instrument Facility (SAIF), Indian Instituteof Technology, Bombay, for 300 MHz NMR spectroscopy is grate-fully acknowledged. T. C. is also grateful to the Council of Scientificand Industrial Research, India for providing fellowship.

Appendix A. Supplementary material

CCDC 792015 and 792016 contain the supplementary crystal-lographic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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