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Macromolecules 1994,27, 3039-3045 3039

Regiochemistry and C onformation of Poly@-hexylthiophene) viathe Synthesis and the Spectroscopic Characterization of theModel Configurational Triad sGiovanna Barbarel la , '*?Alessandro Bongh i ,**$ nd Mass im o Z am bianch itIstitut o dei Com posti del Carbonio Contenenti Eteroatomi e loro Applicazioni, Area RicercaC.N. R., Via Gobetti 101, I-40129 Bologna, Italy, and Dipartime nto di Chimica G. Ciamician,Universith, Via Selmi 2, I-40126 Bologna, Ita lyReceived August 6, 1993; Revised Manuscrip t Received March 7, 1994'

ABSTRACT The four model configurational triads of poly(3-hexylthiophene) PH T) were synthesized bycross-couplingof the approp riate stannyl and bromo 3-hexylthiophenederivatives, catalyzed by Pd[(CsHhPl4.The comparison of lH and 13CNMR chemical shifts of the triads with those of PH T allows the unambiguousassignmentof the regiochemistry of the polymer. The NM R data of the tr iads, in conjunction with the resultsof force field MMPP calculations, also give information on the conformational properties of PHT samplesof different regiochemistry.a-Conjugated oligo- and polythiophenes ar e currentlyreceiving considerable attention in research on co nductingpolymers and molecular electronics. Th e interest isespecially directed toward the introduction of side chainsfor solubility improvem ent an d th e building up of regio-regular str uct ure s or th e modulation of the electrical andoptical properties of these materials.'The re is experimental evidence that the substitutionpattern, Le., the regiochemistry, of substituted poly-thiophenes controls their con formational features, which,in tur n, govern the degree of T-T conjugation betweenadjacent rings, and hence the electrical and opticalprop erties of th e polymers.' An unam biguo us way ofestablishing the regiochemistry of a substituted poly-thiophene is through t he synthesis of the correspondingconfigurational triads2 and the comparison of theirspectroscopic features ('H and 13C NM R, in particular)with those of the polymer. Th e model triads, which are

four different regioisomers of trisubstituted 2,2':5',2"-terthiophene (c f . Chart 11, epresent all the possible modesin which a central 3-substituted thiophene un it can be&,a'-coupled o two similar units via he 2- an d 5-positions,either head-to-tail (H T) , ail-to-tail (TT), r head-to-head("1 So far, no attem pts have been made to synthesize theconfigurational triads of substituted polythiophenes. Inprinciple, a variety of conditions could be employed forthe synthesis of the triads, startin g from 3-substitutedthiophe ne and generating new carbon-carbon bonds bynickel- or palladium-catalyzed cross-coupling of thienylbromides with thienyl organometallicssuch aszinc, oronicacid, and t in rea ge r~ ts.~ lthough organotin reagents areextensively employed due to their synthetic p ~ te n ti a l , ~they have been scarcely used in th e synthesis of sub stitutedoligothiophenes. Th e more generally employed reactionfor the preparation of oligothiophenes is the cross-couplingof thienyl bromides with thienylmagnesium bromides inthe presence of nickel ~ a ta ly s ts .~his reaction, however,gives very low yields when t he thienyl derivatives to becross-coupled bear long alkyl chains next t o the reactionsite.Reported herein is th e synthesis, based on th e use of tinderivatives, of th e model triads (compou nds 1-4) of poly-t IstitutodeiCompostidel Carbonio Contenenti Eteroatomi e lor0Applicazioni.3 Dipartimento di Chimica G. Ciamician,Universitll di Bologna.*Abstract published in Advance AC S Abstracts, April 15,1994.

0024-9297/94/2227-3039$04.50/0

Chart 1. Configurational Triads of Poly(3-R-thiophene)R

R

(3-hexylthiophene) (PHT), which is one of the mostinvestigated polythiophenes because of it s peculiar sol-vatochromic an d thermochromic properties.6 A few papershave been recently published describing new syntheticroutes for the preparation of various versions of thispolymer having different physicochemical p r~ p e rt ie s. ~ -l ~In th is paper th e 13C and 'H NM R chemical shifts oftriads 1-4 are used to establish the regiochemistry of asample of poly(3-hexylthiophene) prepar ed by oxidativepolymerization of 3-hexylthiophene with ferric chlorideand to discuss the substitution p attern of a regiorandomversion of P H T whose 13C and lH NM R chemical shiftshave recently been reported.' Also given in this paper ar ea few indications, based on NMR da ta and supported byMM P2 calculations, about th e conformational propertiesof 1-4 and of th e corresponding con figurational segmentsin poly(3-hexylthiophene).

Resu l t s an d Di scuss ion(I) S y n t h e s i s a n d S p e c t r os c o p ic C h a r a c t e r i z a t i o nof the Conf igu ra t i ona l Triads of Poly(3-hexyl -thioph ene) . Th e synthetic method used for the synthesisof triads 1-4 is outlined in Scheme 1 and is based onselective mono- and dibromination of 3-hexylthiophenewith N-bromosuccinimide in chloroform, selective meta-lation of 3-hexylthiophene with Bu Li/TM ED A followedby quenching with trime thyltin chloride andcross-couplingof t he tin derivative with th e appropriate thienyl bromidein the presence of tetrakis(tripheny1phosphine)palladium.T he cross-coupling eaction affords nonnegligibleamountsof produ ct form ed by homocoupling of th e tin derivative.Purification of the reaction m ixture, which may also involve

0 1994 American Chemical Society


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3040 Barbarella e t al. Macromolecules , Vol. 27 , No. 11, 1994Scheme 1. Synthesis of Triads 1-4 [R = (CHz)&H3]

Table 1. 'H Chemical Shifts. of the Aromatic Region of theModel Triads of PHT (1-4)

2

TT-"(1) H5 H3 H3'6.7'7 6.99 7.00HT-"(2) H5 H4 H3'7.15 6.93 6.98TT-HT(3) H5 H3 H3'6.76 7.00 6.96HT-HT(4) H5 H4 H3'7.12 6.90 6.92a In ppm, in CDC13.

H4"6.95H4"6.95H3"6.94H3"6.96

H5"7.27H5"7.30H5"6.86H5"6.87

separation of different regioisom ers,could only be achievedby flash chromatography using reverse phase R P 1 8 silicagel. Th e 'H and I3C chemical shifts, in deuteriate dchloroform, of the aromatic region of 1-4 are given inTables 1 nd 2, respectively. Figure 1 hows the aromaticregion of the 2D HETCOR spectra of the model triadsand illustrates th e connectivity pat ter n existing betweenth e 'H an d the 13C spectra of these regioisomers.The assignment of H3', the proton belonging to thecentral unit of compounds 1-4, is straightforward, sinceit gives rise to the only singlet present in the s pectrum.Table 1 hows tha t its chemical shift varies within a verysmall range (6.92-7.00 ppm ) when th e type of a,a' linkagewith the adjacent thiophene units changes from HT toTT or HH . Th e assignment of the remaining aromaticprotons of 1-4 is made on the basis of the well-knownfeatures of thiophene derivatives, according to whichprotons separated by three bonds, such as H4,H5 or H4",H5", are characterized by 3 J ~ ~oupling constants on th eorder of 5 Hz, while protons separa ted by four bonds, suchas H3,H5 or H3'',H5", are char acteriz ed by 4 J ~ ~ouplingcons tants on th e order of 2-3 Hz. T he assignment of thecarbon resonances of 1-4 is not as easy as t ha t of protonresonances. A first assignme nt was made on the basis ofthe chemical shifts of the three diads of P H T , namely,3,3'-, 3,4 '-, an d 4,4'-di(3-hexy1)-2,2'-bithiophene,llnd thenchecked with the aid of 2D HETCOR experiments (cf.Figure 1). Furthermore, the assignment was confirmedby HMQC and HMB C inverse-detection 13C NMR ex-periments.12As already observed,l3 h e 13C chemical shiftsof oligothiophenes are insensitive to th e conjugation degreeof these systems but are very dependent on the positionof the alkyl substitu ents. Th us, 13CNM R is an extremely

3

4useful technique t o establish the regiochemistry an d th econformation of oligothiophenes.Table 2 shows tha t th e change of the type of a,a'linkageleads to variations of th e chemical shifts of al l of th e fourcarbons of th e central unit of 1-4, which are much greaterth an those observed in proton spectra. Moreover, it isseen th at a configurational change-in one or the othe r ofth e two linkages-of th e type TT - T (such as thatneeded to pass from 1 o 2 or from 3 to 4) or H H - T(such as tha t needed to pass from 1 o 3 or from 2 to 4),leads to 6(13C) increments which ar e almost in depe ndentof the natu re of the adjacent junction. This is summarizedin Scheme 2, which gives th e sign and th e magn itude of6(13C) ncrements for the HT - T, HH - T , TT-HT, and HT - H configurational changes occurring inon e or the o ther of the two junctions. I t should be noticedth at th is scheme allows the prediction of the 13C NMRspectrum of the aromatic region of PHT in all itsregiochemically different forms.(11) Assignment of the Regiochemistry of PH T by'H nd 13CNMR. Figure 2 reports the proton spectrum(in chloroform) of th e aromatic region of a samp le of P H Tobta ined by oxidative polyme rization of 3-hexylthioph enewith ferric chloride, prepared according to the modalitiesdescribed in ref 10. Th e aromatic region of the spectrumconsists of a m ajor peak a t 6.98 ppm, which accou nts forabout 80 5% of th e total signal intensity, and of three minorpeaks of nearly equal intensities at 7.05, 7.03, and 7.00ppm. Th is spectrum has the same chemical shifts and thesame relative peak intensities as those reported by Sat0e t al . fo r a samp le of electrochemically prepared poly(3-dodecylthiophene)(PDDT).2It ha s also he sam e chemicalshifts (b ut not th e same relative intensities) as t he spectrumof a regiorandom sample of PH T 7an d of different samplesof PHT obtained with diverse synthetic methods.'0J4Comparison of the proton chemical shifts of our PHTsample with th e values of th e chemical shifts of th e H3'proton of th e four configurational triads, reported in Table1, shows th at all the protons of the polymer sample ared e s h i e l d e d by about 0.05 ppm with respect to the H3'protons of triads 1-4. T he constanc y of th e deshieldingeffect suggests tha t th e assignment of the peaks of theP H T sample to t he four configurations should follow thesame order as t ha t observed for compounds 1-4 Le., t ha tthe major peak a t 6.98 ppm should be attrib uted to the


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Macromolecules, Vol. 27, No . 11,1994 Conformation of Poly(3 -hexylthioph ene) 3041

BP

1. 87, s7.41. 3- .21. 17 .01, s8 . 18. 71 .88. 53 .4

1 - i

f l lP*

1.) .8 . 8 -8 . 7 .1,8 - ,1.1 .

7 . 1

7 . 0

\' I '

l . B -1.7 .1 . 6 -

11 4 iI 2 110 118 l a 8 1 3 4 1n 3 ii o t i l ,I: la 1 11 4 11) 110 118 t i c 11 4 d o d o ti nr2 IPW ?I mr

Figure 1. Two-dimensionalHETCOR pectraof the arom atic region of model triads 1-4, illustrating he proton-carbon connectivitiesof th e four regioisomers.

TT-HH (1) 137.1 124.9 144.1 118.9 137.3HT-HH (2) 130.9 139.4 130.0 123.4 135.9TT-HT (3) 136.9 124.8 144.1 118.9 135.2HT-HT (4) 131.0 139.5 130.0 123.5 133.9

Table 2. *9c Chemical Shifts. of the Aromatic Region of the Model Triads (1-4) of PETc2 c3 c4 c5 C2' C3' C4' C5' C2" C3" C4" C5"124.9 143.1 127.5 128.4 142.5 128.6 125.4127.3 142.6 128.6 128.5 142.5 128.6 125.5126.2 139.9 129.8 135.7 127.1 143.6 119.9128.6 139.5 130.7 135.6 127.1 143.6 120.0

a In ppm, in CDC13.Scheme 2. 'SC Chemical Shift Increments (in ppm ) ofthe Central Unit of Triads 1-4, Following aConfigurational Change H- or T - H n One of th eTwo Adjacent Junctions..

2

4 HT-HT 1TT-" 1l-r-m

3a The incrementa are those relative to C2', C3', C4', and C5'(from top to bottom).

HT-HT configuration, th e one a t 7.00 ppm t o the TT-H T configuration, the one a t 7.03 ppm t o the HT-HH

configuration, and the one at 7.05 ppm to the TT-HHconfiguration. Th is assignmen t is in agreem ent with tha tmade by Holdcroft et a1.* on the basis of qualitativeargume nts on conformation-dependent ring curre nt effectson the WH) values of the aromatic region of PHT.However, they are in contrast w ith other authorssJ* as faras the assignment of TT -HT and HT-HH configurationsis concerned. Thu s, up to this point, a margin of ambiguityin the assignm ent of th e different configurational portionsof P H T by proton NMR still exists. However, th eambiguity can be removed by looking a t the 8(13C) aluesof PHT, which are insensitive to ring c urren ts affectingproton chemicalshifts. In the W spectrum of the aromaticregion of our P H T sample, which is the same as thatreported by other a ~ t h o r s , ~ ~ J ~nly the four signalspertaining t o the major compo nent of th e polymer (139.9,133.8,130.5, and 128.7 ppm ) areclearly assignable whereassome of the signals pertaining to the minor compo nentsare not sufficiently intense. However, th e I3C spectrumof the arom atic region of P H T in its four differentconfigurations has been recently reported by Riecke eta1.,7 who have been able to pr epare a totally regiospecific


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3042 Barbarella et al. Macromolecules, Vol. 27, No. 11, 1994

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Macromolecules, Vol. 27,No . 11, 1994 Conformation of Poly(3 -hexylthioph ene) 3043picture of 1-4 given by MMPB calculations for E = 5 istrustworthy.Conclusions

The synthesis and he lH and I3C NMR characterizationof th e four model configu rational triads of poly(3-hexyl-thiophene) allow the unambiguous assignment of theregiochemistry, i.e., of the substitution pattern, of thepolymer and, in conjunction with force field MMP2calculations, also gives information on th e conform ationalcharacteristics of its differ ent configurational segments.Th e data reported in this paper show that the regio-chemistry of poly(3-hexylthiophene) ha s a great influenceon its conformational properties. Poly(3-hexylthiophene)samples containing he ad-to-tail linkages are characterizedby the greatest conformational variability, while thepresenc e of head-to-he ad linkag es implies a more restr ictednumb er of conformations bu t larger inter-ring twist anglesan d conjugation interruptions . Th e presence of segmentswith adjacent head-to-tail/head-to-head linkages impliesconformational stabilization through side chain interac-tion. The se findings explain why regiochemically differ entversions of p oly(3-hexylthiophen e) display very differe ntelectrical an d optical properties, as recently reporte d byRiecke an d co-workers for a regiospecific head-to-tail anda regiorandom sample of th is p ~ ly m e r . ~Experimental Section

Gener al Procedures . n-Butyllithium (2.5 M in hexane),3-bromothiophene,N-bromosuccinimide and t etrak is(triphen -y1phosphine)palladium (Pd[(c& )P s]r ) were purchased fromJanssen. [1,3-Bis(diphenylphosphino)propane]nickel(II)hlo-ride (NiClz(dppp)),rimethy ltin chloride,and lithium wire werepurchased from Aldrich Chimica. All solvents used in reactionsand chromatographies were distilled from appropriate dryingagents before use. Analitical TLC was performed by using 0.25-mm silica gel plates (M erck), nd visualization was accomplishedby UV light. Flash chromatographies were carried ou t on silicagel (230-400mesh ASTM) or reverse phase R P 18 (230-400 meshASTM). The mass spectra were determined using a Varian MAT11 2 S mass spectrometer equipped with a Vianello 9.8.8. datasystem. UV spectra were obtained using a Perkin-Elmer 554spectrometer. Boiling points are uncorrected. lH NMR spectrawere recorded a t 200 MHz with a Varian VXR 200 spectrometer,using TMS (6 = 0.0 ppm) as the internal reference in CDC13solutions. 13CNM R spectra were recorded a t 50 MHz with thesame spec trometer, using CDC13 (6 = 77.0 ppm) as the internalreference in CDC13 solutions. 13Cchemical sh ift assignments ofcompounds 1-4 were made on the basis of 2D HETCORexperiments to establish proton-carbon connectivities andconfirmed by HMBC and HMQC experiments.l2 Molecularmechanics MMP2 calculations were performed using the AllingerMM2(91)19program with a Va x Station 2000.4,4,3-Tri(3-hexyl)-2,2:5,2-terthiophene1). 3-Hexyl-thiophene (la). A 50-mL round-bottom ed flask was chargedwith 5.41 g (0.23 mol) of magnesium turnings, and a solutionof33 g (0.2 mol) of 1-bromohexane in 100 mL of anhydrous ethylether wa s added under an argon atmosphere. The mixture wasstirred at 0 C (ice bath ) for 30 min and then allowed to warmto room temperature. A solution of 32.6 g (0.2 mol) of 3-bro-mothiophene and 0.217 g (0.4 mmol) of NiClZ(dppp) in 100mLof ethyl ether was added, and the mixture was allowed to refluxfor 2 h, hydrolyzed with a solution of 2 N HC1, washed with a10% solutionofNaHC03,and extracted with ether. The organiclayer was washed twice with brine, dried over MgSOd, and thenevaporated, and 23.5 g (70%) of a 97:3 3-hexylthiophene-dodecane mixture ( la ,by lH NMR analysis) was obtained,whichwas used without further purification. lH NMR (200 MHz,CDCb, ppm): 7.2 (m, 1H); 6.9 (m, 2 H); 2.6 (t , 2 H); 1.6 (m, 2H); 1.3(m,6 H); 0.9 (t ,3 H). l3C NMR (50MHz, CDCl3, ppm):143.2; 128.2; 125.0; 119.7; 31.7; 30.6; 30.3; 29.0; 22.6; 14.1.2-Bromo-3-hexylthiophene lb). To a solution of 6.22 g (37mmol) of la in 60 mL of 1:lCHC13-CH3COOH was added 6.94

Figure 3. Preferred conformation of triad 2 (from MMP2calculations a t e = 5 and e = 1.5).properties, 13C NMR da ta a nd MMPB calculations indicatethat a triad may be considered as being the sum of twoalmost independent bithiophene subsystems.A striking feature of Table 3 s tha t th e energy differencebetween the two anti-a nti conformers of the HT -HH triad,2, is 2 kca l mol-, wh ile for 1 ,3 ,and 4 th e energy differencebetween the two anti-anti conformers is 1 order ofmagnitude smaller. Examination of the factors contribut-ing to the total energy shows that this is due to thestabilization of one of th e two anti -a nt i conformers of 2by long-range van der Waals interactions. As shown inFigu re 3-which gives th e prefe rred conforma tion of tria d2-the chains belonging to the termin al rings are locatedon th e same plane and are converging, with th e averageH-H, C-H,nd C-C distan ces being o n th e orde r of 3.5-5A. I t is th e sum of small an d stabilizing H-H, C-H, an dC-C van der W aals interactions which gives rise to th ecalculated energy differences between th e tw o ant i -ant iforms for E = 5 as well as for e = 1.5. It mu st be stressedth at th e conformation reported in Figure 3 is the prevailingone (>go%) for both values of the dielectric constant,contrary to w hat is observed not only for 1 , 3 , and 4 bu talso for a series of m ethyl-s ubstitute d 01igothiophenes.l~Thus, 2 is an example of conformational preferencedominated by long-range interactions between the alkylchains.T h e UV absorption maxima, Am of 1-4 are reportedin Table 3. All compounds have a Am value smaller tha nthat of unsubstituted terthiophene (Am = 355 nm5bJ6)despite the bathochromic effect which should be exertedby the alkyl groups. In consequence, as indicated byMMPB calculations, the backbone of the four triad s is notplanar bu t tilted t o a different exte nt as a result of th esteric effects of the substituents. It should be noticedth at there is a large difference (33 nm ) in the Am valuesof the four compounds and th at th e Am value of triads1 an d 2, having a H H junction, ar e smaller than those oftriads 3 and 4. Th is is accounted for by the greater inter-ring twist angle of the H H linkage compared to th at of H Tor TT linkages, which causes a decrease in a - a*conjugation. For a semiqu antitative check of the validityof MM P2 calculations, we have calculated th e Am of 1-4using th e Pariser-Parr-Pople approach17 n d multiplyingthe @ resonance integral bonds by cos2 w , where w are theMMPB calculated inter-ring twist angles fo r th e prevailingconform ations of 1-4. T he rationale behind th is procedureis that, according o Bredas et a1.,18 he electronic propertiesof oligothiophenes are well fitted by a cos2 unction of th etorsion inter-ring angle w . Although the absolute valuesof Am, calculated in this way are somewhat different (bu tof th e same order) from experimental ones, the tren d ofvariation on going from 1 to 4 is the same as that foundexperimentally. This indicates tha t the conformational


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3044 Barbarella e t al. Macromolecules, Vol. 27, No. 11 , 1994with R P 18 silica gel and 8:2 CH30H:CHZClz as the eluent gave0.37 g (5 1% )of 1 as a pale yellow oil. MS , m/e 500 ( M + ) ;(CHC13): 326 nm. lH NM R (200 MHz , CDC13, ppm ): 7.27 (d ,1H ); 7.0 (s, 1H) ; 6.99 (d, 1H); 6.95 (d, 1H) ; 6.77 (m , 1H) ; 2.5(m, 6 H) ; 1.5 (m, 6 H ); 1.3 (m, 18 H); 0.9 (m , 9 H). 13C NMR (50MH z, CDC13,ppm ): 144.1; 143.1; 142.5; 137.3; 137.1; 128.6; 128.4;127.6; 125.4; 124.8; 118.8; 31.7; 30.7; 30.6; 30.5; 30.4; 29.1; 29.0;28.9; 22.6; 14.1.3,4,3-Tri(3-hexyl)-2,2:5,2-terthiophene2). 2,5-Dibromo-3-h exy lthi oph en e (2a). To a solution of 5.04 g (30 mmol) of lain 12 0 mL of 1:lCHC13:CH3COOH was add ed 11.24 g (63 mmo l)of N-bromosuccinimide. Th e mixture was stirred for 30 min,and then 120 mL of distilled water was added. The m ixture wasfirst washed with a 10% KOH solution and then with water,dried over MgS04, and evaporated. After flash chromatography(silica gel, hexane), 6.94 g (7 1% )of 2 a was obtain ed as a yellowoil. lH NM R (200 MH z, CDCl3, ppm ): 6.76 (s, 1 H); 2.49 (t ,2H) ; 1.5 (m, 2 H); 1.3 (m, 6 H); 0.88 (t ,3 H). 13C NM R (50MHz,CDC13, ppm ): 143.0; 131.0; 110.3; 107.9; 31.6; 29.5; 29.4; 28.8;22.6; 14.0.3,43-i(3-hexy1)-2,2:5,2-terthiophene 2). T o a solu-tion of 0.582 g (1.76 mmol) of 2-(trimethylstannyl)-3-hexyl-thioph ene in 30 mL of toluene was adde d a solution of 0.287 g(0.88mm ol) of 2,5-dibromo-3-hexylthiophene n 30 mL of toluenecontaining also lOmg (0.009mmol)of P d[ (C6&,)3]4.The mixturewas allowed to reflux for 4 h, hydrolyze d with 2 N HCl, neutralizedwith a 10% solution of NaHC03, washed twice with brine, driedover MgS0 4, and evaporated . Flash chromatography with RP18silica gel an d 8:2 CH30H:CHzClz as th e elu ent gave 0.11 g (0.2mmo l, 24 % ) of 2 as a pale yellow oil. MS , mle 500 ( M +) ;A(CHC13): 315 nm. lH NMFt (200 MHz , CDC13, ppm ): 7.30 (d,1H) ; 7.15 (d, 1H) ; 6.98 (8,1H) ; 6.95 ( d, 1H); 6.93 (d, 1H ); 2.8(m, 2 H) ; 2.5 (m, 4 H ); 1.6 (m, 6 H ); 1.3 (m, 18 H) ; 0.9 (m, 9 H) .l3C NM R (50MH z, CDC g, ppm ): 142.6; 142.5;139.4; 135.9; 130.9;130.0; 128.6; 128.5; 127 .3; 125.5; 123.4; 31.7; 30.8; 30.7; 30.6; 29.3;29.2; 29.1; 28.9; 22.6; 14.1.4,4,4-i(3-hexyl)-2,2:5,2-terthiophene (3). To a solu-tion of 0.49 g (1.51 mmol) of 2,5-dibromo-3-hexylthiophenen 50mL of toluene was add ed a solution of 1g ( 3 mmo l) of 3-hexyl-5-(trimethylstanny1)thiophene nd 17 mg (0.015 mmol) of Pd-[ C6HS)3P]4. The mixture was allowed to reflux for 4 h , hydrolyzedwith 2 N HCl, neutralized with a 10% solution of Na HC03 ,washedtwice with brine, dried over MgS04, and evaporated. Flashchromatography with R P 18 silica gel and 8 2 CH30H:CHzClz a sthe eluen t gave 0.2 g (2 7% )of 3 as a pale yellow oil. MS , m /e500 (M+);A (CHC13): 348 nm. lH NM R (200 MH z, CDCl3,ppm): 7.00 (d, 1H) ; 6.96 (s, 1H) ; 6.94 (d, 1H ); 6.86 (1H); 6.76(1H ); 2.7 (m, 2 H) ; 2.5 (m, 4 H ); 1.6 (m, 6 H ); 1.3 (m, 18 H); 0.9(m , 9 H). l3C NM R (5 0 M Hz, CDCl3, ppm ): 144.1; 143.6; 139.9;136.9; 135.7; 135.2; 129.8; 127.1; 126.2; 124.8; 119.9; 118.9; 31.7;30.5; 30.4; 30.3; 29.4; 29.2; 29.0; 22.6; 14.1.3,4,-Tri(3-hexyl)-2,2:5,2-terthiophene (4). 3,4-Di(3-hexyl)-2,2-bithiophene (4a). A solution of 2-bromo-3-hexyl-thiophene (2 g, 8 mmol) in 30 mL of toluene was added to asolution of 3-hexyl-5-(trimethylstannyl)thiophene (2.65 g, 8mmol) in 50 mL of toluene containing 92 mg (0.08 mmol) ofPd[(CsH5)3P]4. Th e m ixture was allowed to reflux for 20 h andthen hydrolyzedwith ice cold 2 N HC1, neutralized with NaH C03,and extracted with ether. Th e organic layer was washed twicewith brine, dried over MgSO4, and the n evaporate d. Flashchromatography (silica gel RP 18/9010 CH30H:CH&12) gave0.61 g (2 3% ) of 4a as a pale yellow oil. MS m le 334 ( M + ) . HNM R (200 MH z, CDCl3, ppm): 7.10 (d, 1H) ; 6.93 (d, 1H) ; 6.88(d , 1 H); 6.85 (m, 1H) ; 2.7 (m , 2 H); 2.5 (m, 2 H); 1.6 (m, 4 H );1.3 (m, 12 H) ; 0.9 (m , 6 H) . 13C NM R (50 MH z, CDC13, pprn):143.5; 139.3; 135.9; 131.0; 129.6; 127.3; 123.4; 119.9; 31.7; 31.6;30.7; 30.5; 30.4; 29.2; 29.1; 29.0; 22.5; 14.1.3,4-Di(3-hexyl)-6-bromo-Z,Z-bithiophene4b). T o a solu-tion of 0.5 g (1.5 mmol ) of 3,4-di(3-hexyl)-2,2-bithiophenen 40mL of CHC13at 0 C (ice bath) was adde d 0.266 g (1.5 mmo l) ofN-bromosuccinimide. Th e mixture was stirred for 30 min, andthe n 40 mL of distilled wa ter was added. Th e mixture was firstwashed with a 10% KOH solution and then with water, driedover MgS 04,and evaporated. After flash chromatography (silicagel, hexane ), 0.607 g ( 9 8 % )of 4b was obtaine d as a pale yellowoil. 1H NM R (200 MHz, CDC13, ppm): 7.12 (d, 1H); 6.89 (d, 1

g (39 mmol) of N-bromosuccinimide. Th e mixture was stirredfor 30 min, and then 60 mL of distilled water was added. Th emixture was first washed with a 10% KOH solution and the nwith water, dried over MgS04, an d evaporated. After distillation(127 C, 7 mmHg), 8.5 g (93 %) of l b was obtained. lH NM R(200 MH z, CDC13, ppm ): 7.1 (d, 1H) ; 6.7 (d, 1H) ; 2.6 (t, 2 H );1.6 (m , 2 H) ; 1.3 (m, 6 H ); 0.9 (t ,3 H ). 13C NM R (50 MHz , CDC13,ppm ): 141.9; 128.2; 125.1;108.8;31.6; 29.7; 29.4; 28.9; 22.6; 14.1.2- (Trim ethy l s tanny l ) -3 -hexy l t iophene ( IC) . A 100-mLround-bottom ed laskwas charged with 1.76g (0.25mol) of lithiu mwire and 10 mL of anhydrou s TH F at -10 C, and the n a solutionof 5 g (25 mm ol) of trim ethylti n ch loride in 40 mL of T H F wasadded in two steps. The mixture was warmed to room tem-perature a nd stirred overnight. Then 8.1 mL (4.05 mmol) of thissolution (0.5 M (trimethy1stmnyl)lithium) as added to a solutionof 1 g (4.05 mm ol) of 2- bromo-3 -hexylthiophe ne a t roomtemperature. After 30 min, the solution was quenched withammonium chloride solution, extracted w ith ether, washed withbrine , dried over MgSOd an d evapor ated. A tota l of 1.1g (82%)of IC was obtained, which was used without fur ther purification.1H NMR (200 MHz, CDC13, ppm): 7.50 (d, 1H) ; 7.08 (d, 1H );2.6 (m, 2 H); 1.6 (m 2 H) ; 1.3 (m, 6 H ); 0.9 (t, 3 H) ; 0.4 (s, 9 H).13C NM R (50 MH z, CDC13, ppm ): 150.8 ; 131.2 ; 130.4 ; 129.3; 32.6;32.1; 31.8; 29.3; 22.6; 14.1; -8.0.3,3-Di(3-hexyl)-2,2-bithiopheneId). A solution of 0.457g (1.85 mmo l) of 2-bromo -3-hexylthiop hene n 30 mL of freshlydistilled toluene was add ed t o a solution of 0.612 g (1.85 mmol)of 3-hexyl-2-(trimethylstannyl)thiophenen 30 mL of toluenecontaining 21 mg (0.018 mm ol) of [(CsH5)3Pl4Pd. T he mix turewas allowed to reflux and its ev olution followed by TLC ana lysis.After complete disappeara nce of 3-hexyl-2-(trimethylstannyl)-thiophene, the brownish solution was hydrolized with ice cold 2N HC1, neutralized with NaHC03, and e xtracted with ether. Th eorganic layer was washed twice with brine, dried over MgS04,and then evaporated. Th e residue was purified by flashchromatography (silica gel R P 18/85:15 CH30H:CH&lz), an d0.36 g (59 % )of Id as a colorless oil was obtained. MS, m/e 334(M e+ ). 1H NMR (200 MH z, CDC13, ppm): 7.25 (d , 2 H) ; 6.94 (d ,2 H) ; 2.5 (m, 4 H); 1.5 (m, 4 H); 1.2 (m , 12 H ); 0.8 (m, 6 H) . 13CNM R (50 MHz CDC13, ppm ): 142.3; 128.7; 128.4; 125.2; 31.7;30.7; 29.1; 28.8; 22.6; 14.1.3,3-Di(t-hexyl)-5-bromo-2,2-bithiophenele) . To a solu-tion of 1.1g (3.3 mmol) of 3,3-di(3-hexyl)-2,2-bithiophenen 60mL of 1:l CHC&:CH&OOH was added 0.62 g (3.5 mmol) ofN-bromosuccinimide. T he mixture was stirred for 30 min, andthen 60 mL of distilled water was added. Th e mixture was firstwashed with a 10% KOH solution and then with water, driedover MgS04 ,and evaporated. After flash chromatography (silicagel, hexane), 1.04 g (2.5 mmol, 76% ) of l e was obtained as ayellow oil. 1H NMR (200 MH z, CDC13, ppm ): 7.26 (d , 1H) ; 6.93(d , 1H) ; 6.90 (s, 1H) ; 2.5 (m, 4 H); 1.5 (m , 4 H); 1.3 (m, 12 H) ;0.8 (m, 6 H). 13C NMR (50 MHz, CDC13, pp m) : 143.2; 142.9;131.3; 130.3; 128.6; 127.4; 125.8 ; 111.7; 32.0; 31.7; 31.6; 30.7; 30.5;29.7; 29.4; 29.1; 29.0; 28.8; 28.7; 22.7; 22.6; 22.5; 14.1; 14.0.3-Hexyl-5-(trimethylstannyl)thiopheneI f ) . To a solutionof 3.36 g (20 mm ol) of 3-h exylthiophen e in 100 mL of et hyl eth ercontaining 2.55 g (22 mmo l) of N,N,N,N-tetramethylethylen-diamine was added 8.8mL (2 2 mmol) of BuLi (2.5 M in hexane).The mixture was allowed to reflux for 1h an d then cooled to 0C (ice bath ), and a solution of 4.38 g (22 mm ol) of trim ethyltinchloride in 20 mL of ethyl ether wa s added. The mixture wasallowed to warm to room temperature, quenched with ammoniumchloride solution, washed with brine, dried over NaZSO,, andevaporated, and 5.9 g ( 9 0 % )of I f was obtaine d, which was usedwithout furt her purification. lH NM R (200 MH z, CDC13, ppm ):7.18 (m , 1 H); 7.0 (d, 1H ); 2.6 (m, 2 H); 1.6 (m, 2 H) ; 1.3 (m, 6H) ; 0.9 (t ,3 H). I3C NM R (50 M Hz, CDCl3, ppm): 144.5; 137.1;136.6; 125.7; 31.7; 30.7; 30.0; 29.2; 22.6; 14.1.4,43-Tri(3-hexyl)-2,2:5,2-terthiophene1). To a solu-tion of 0.48 g (1.45 mmol) of 3-hexyl-5-(trimethylstannyl)-thiophene and 1 7 mg (0.0015 mmo l) of Pd[(C& )sP]4 in 30 mLof toluene was added a solution of 0.6 g (1.45 mmol) of 3,3-di-(3-hexyl)-5-bromo-2,2-bithiophenen 30 mL of toluene. Th emixture was allowed to reflux for 4 h, hydrolyzed with 2 N HCl,neutralized with a 10% solution of N aHC 03, washed twice withbrine, dried over MgS04, and evapora ted. Flash chromatog raphy


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Macromolecules, Vol. 27, No. 11, 1994H); 6.78 (8,1H) ; 2.7 (m, 2 H); 2.5 (m, 2 H ); 1.6 (m, 4 H); 1.3 (m,12 H); 0.9 (m , 6 H). 13C NM R (50 MH z, CDCla, ppm): 142.3;139.9; 135.7; 130.0; 129.9; 126.9; 125.8; 108.5; 31.6; 30.7; 29.7; 29.6;29.2; 29.1; 28.9; 22.0; 14.1.3,4,4-Tri(3-hexy1)-2,2:5,2-terthiophene4). T o a solu-tion of 0.48 g (1.45 mmol) of 3-hexyl-5-(trimethylstannyl)-thio phe ne and 17 mg (0.015 mmol) of Pd[(CeH&P14 in 30 mLof toluene was added a solution of 0.6 g (1.45 mmol) of 3,4-di-(3-hexyl)-5-bromo-2,2-bithiophenen 30 mL of toluene. T hemixtu re was allowed to reflux for 4 h, hydrolyzed with 2 N HC1,neutralized with a 10% solutio n of NaHCO3, washed twice withbrine, dried over MgSO4, an d evaporated. Flash chromatographywith RP 18silica gel and 8 2 CH30HCH2C12as the eluent gave0.48 g (69%) of 4 s a pale yellow oil. M S, m l e 500 (M + ) ;A(CHCl3): 336 nm. lH NM R (200 MH z, CDC13, ppm): 7.12 (d,1H) ; 6.96 (d , 1H) ; 6.92 (9, 1H) ; 6.90 (d, 1H) ; 6.87 (m , 1H) ; 2.7(m, 4 H); 2.6 (m, 2 H); 1.6 (m, 6 H) ; 1.5 (m, 18H); 0.9 (m , 9 H).l3C NM R (50 M Hz , CDC b, ppm): 143.6; 139.5; 135.6; 133.9; 130.7;130.0; 128.6; 127.1; 123 .5; 120.0; 31.7; 30.7; 30.6; 30.5; 30.4; 29.3;29.2; 29.0; 22.6; 14.1.Poly (3-h exyl thiop hene ). Poly(3-hexylthiophene) was pre-par ed by chemical polymerization of 3-hexylthiophene (l g, 0.006mol, in 40 mL of CHCl3) with dry FeC13 (3.87 g, 0.024 mol, insuspension in 100 mL of CHCl3) according to the modalitiesdescribed in ref 10. The reaction mixture was stirred overnightat room temperature and then worked u p with MeOH, and thepolymer was extracted with a Soxhlet apparatu s using methanol(1night) and acetone (1night). Th e black solid was dried undervacuum an d then repea tedly washed using a hydrazine solution(2% w/w in water). Th en the aqueous phase was filtered, andthe solid was dissolved in T H F an d precipitated again usingMeOH. Th e yield was 45%. A (CHCl3): 437 nm . l3C NM R(CDC13, T M S, p pm): 139.8; 133.8; 130.5; 128.7; 32.0; 30.5; 29.3;22.5; 14.2.

Conformation of Poly(3-hexylthiophene) 3045(3) Tour, J. M.; Wu, R. Macromolecules 1992,25,1901. Snieckus,V. Chem. Rev. 1990,90,879.(4) Stille, J. K. Angew. Ch em., Znt. Ed . Engl. 1986, 25, 508.(5) (a) Tamao, K.; Kodama, S.; Nakajima, I.; Kumada, M. Te t -rahedron 1982,38,3347. (b) van Pham, C.; Burkh ardt, A.;Shaba na, R.; Cunningham, D. D.; Mark, H. B., Jr.; Zimmer, H.Phosphorus, Sul fur, Silicon 1989,46, 153.(6) Rughooputh, S. D. D. V.; Hotta, S.; Heeger, A. J.; Wudl, F. J.Polym. Sci.: Part B Polym. Phys. 1987,25,1071. Inganas, 0.;Salaneck,W. R.; Osterholm,J. E.; Laakso,J. Synth. Met. 1988,22,395. Salaneck, W. R.; Inganas, 0.;Thema ns, B.; N illson,J.0.;jogren, B.; Osterholm ,J. E.; Bredas, J. L.; Svensson,S. J.

Chem. Phys. 1988,8 9, 4613. Them ans, B.; Salaneck, W. R.;Bredas,J.L. Synth.Met . 1989,28,C359. Bi,X.;Ying, Q.;Qian,R. Makromol. Chem .,Macromol. Chem.Phys. 1992,193,2905.Goedel, W. A.; Somanathan, N. S.; Enkelmann, V.;Wegner,G.Makromol. Chem., Macromol. Chem. Phys. 1992, 193, 1195.(7) Chen, T. A.; Rieke, R. D. J. Am. Chem. SOC. 992,114,10087.( 8 ) Mao, H.; Xu, B.; Holdcroft, S. Macromolecules 1993,26,1163.(9) McCullough, D.; Lowe, R. D.; Jayraman, M.; Anderson, D. L.J . Org. Chem. 1993,58, 904.(10)Souto Maior, M.; Hinkelmann, K.; Eckert, H.; Wudl, F.Macromolecules 1990,23 , 1268.(11) Barbarella, G.; Zambianch i, M., unpublished re sults.(12) Inverse-detected13C D HMQC and H MBC NMR experimentswere carried out by Prof. Luisa Schenetti, Dipartimento diChimica,UniversitA di Modena , Italy. We are grateful to Prof.Schenetti for letting ua know her results prior to publication.(13) Barb arella , G.; Bongini, A.; Z ambianch i, M. Ado. Mater. 1991,3,494. Arbizzani, C.; Ba rbarella, G.; Bongini,A.; Mastragostino,M.; Zambianchi,M. Synth. Met . 1992,52,329. Barbarella, G.;Bongini, A.; Zamb ianchi, M. Tetrahedron 1992,48,6701.(14) Leclerc, M.; Martinez Diaz, F.; Wegner, G. Makromol. Chem.1989,190,3105.(15) Sato, M.; Shimizu, T.; Y amauchi, A. Makromol. Chem. 1990,191, 313.(16) Martinez.F.:Voelkel.R.:Naeeele.D.:Naarmann,H.ol .Cwst.

References an d Notes(1) Roncali, J. Chem. Rev. 1992,9 2, 711.( 2 ) Sato, M.; Morii, H. Macromolecules 1991,24,1196. Sato, M.;Morii, H. Polymer Commun. 1991, 32, 42.

. . I . .Liq. Cryst. 1989, 167 , 227.2022.(17) Lathi, P.M.; Obrzut, J.; Karasz, F.E. Macromolecules 1987,20,(18) ?ximans, B.; Salaneck, W. R.; BrBdas, W. R. Synth.Met . 1989,

(19) Q uantum Chemistry Program Exchange,University of In diana,29, C359.Bloomington, IN 47405.

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